text:
Bitcoind (linux) CPU usage through the roof
Basically I'm trying to keep a wallet on linux along with the RPC service so I can receive coins and poll the server periodically for transactions.
I'm trying with both 0.8.1 and 0.8.5 and CPU usage is at 100%, running this on amazon and I get the same even with the xlarge EC2 instance. This has been going on for over 24 hours, had to force reboot the instance to be able to reconnect.
It's not even set to generate coins. gen=0
I guess I'd like to know if this is permanent, or a bug, or something I'm doing wrong? Or maybe it just takes a while to "sync" or whatever its doing then it will go back to "normal" and by normal I mean any level of CPU usage that isn't in the range of WTF and OMG.
Also tried sending myself some 0.01-0.05 btcs and they never made it. Maybe it takes a while to show up? Although blockchain says said transactions have over 100 confirmations.
TIA

From the description you are giving it sounds like you haven't yet synchronized with the network. Before you can start doing anything useful, e.g., see your current balance, the bitcoind client downloads the entire blockchain and verifies it. This may take quite some time and will likely keep your CPU busy until its done. You can check the progress of the synchronization by issuing a bitcoind getinfo and checking the blockchain height with blockchain.info or similar site.

Thank you so much for confirming. Thought it might be something like that.

Change ~/.bitcoin/bitcoin.conf
daemon=1

to
daemon=0

And use this utility cpulimit:
$ cpulimit -l 10 bitcoind

This way you set bitcoind to use no more than 10% of CPU:
$ cpulimit -h
CPUlimit version 1.7
Usage: cpulimit TARGET [OPTIONS...]
   TARGET must be exactly one of these:
      -p, --pid=N        pid of the process
      -e, --exe=FILE     name of the executable program file
                         The -e option only works when
                         cpulimit is run with admin rights.
      -P, --path=PATH    absolute path name of the
                         executable program file
   OPTIONS
      -b  --background   run in background
      -c  --cpu=N        override the detection of CPUs on the machine.
      -l, --limit=N      percentage of cpu allowed from 1 up.
                         Usually 1 - 400, but can be higher
                         on multi-core CPUs (mandatory)
      -v, --verbose      show control statistics
      -z, --lazy         exit if there is no suitable target process,
                         or if it dies
      -h, --help         display this help and exit

Look at this question:
What are the alternatives to downloading the 6GB block chain?


text:
Is Butterfly Labs reputable / Should I preorder the SC Jalepeno?
I'm somewhat new to the mining scene but I'm a bit familiar with everything. I see that GPU mining will become much less cost effective over the next year or so, especially around December when the block reward size drops to 25 BTC.
As an entry level miner, I don't have a decent rig to just use a pool with or anything. I'm stuck with a quad core AMD mobile CPU in an HP laptop with the worst ATI card known to mankind, giving me about 7.5 Mh/s using rpcminer-4way. Based on what I've seen, the claims that Butterfly Labs is making are pretty substantial and if they're true, they could greatly change the playing field. At a price as low as $150 for 3 Gh/s, I would be willing to invest, since I don't have the money right now to build a GPU mining machine.
I have seen many people preorder the SC Jalepeno model and I'd just like some additional info and background on the company and their products before shelling out $150-$300. And are there any comparable low-cost FPGA or ASIC USB devices with a decent Mh/s/$?

Are they already up for pre-ordering?? I subscribed to Butterfly Labs newsletter but didn't know they were taking pre-orders already. Are you sure? About the question, there's a lot of speculation going on on whether their specs and price are real or just a scam.

I saw them now. Didn't notice it last time. Don't have time for research today but will probably check what the folks on BitcoinTalk are saying about this.

It's not clear that the block reward dropping will affect GPU mining's effectiveness.  It's possible that the dollar price of a bitcoin may rise enough to counteract the reward halving.  And even if it doesn't, some miners will stop mining, leading to a reduction in the difficulty of mining.  It remains to be seen what actually happens of course.

@ChrisMoore: The block reward halving will affect profitability, difficulty and price. The product of all these factors is 2, so the simplest theory is that each will change by a factor of the cube root of 2.

EDIT:
My original answer may have made sense back when the question was asked, but now it is clear that Butterfly Labs cannot be trusted.
As they say, "fool me once, shame on you; fool me twice, shame on me". After all the delays and controversies with their FPGA line, they have given their word that with the experience gained they really will be able to deliver their ASIC line on October 2012. 10 months later (and 20-fold difficulty increase later), even the first pre-orderers didn't get their orders in full. This didn't stop them from announcing a new line, with pre-orders and the same empty promises. Which, if they deliver, will be better performing than their first ASIC line, without any compensation to their loyal customers who have waited more than a year.
The fact that their CEO was shown to be a convicted felon doesn't help.

Care to link to "CEO shown to be a convicted felon"?

@Pacerier: ETA a link to a forum post discussing it, which itself has links to other resources.

So those products promised to be delivered 3 years ago all weren't delivered? No one saw a single BFL product?

@Pacerier: That's not what I said. The edit was made on August 2013 and read "in full", meaning orders were partially delivered. Now we're at 17 months (not 3 years) after October 2012, and I believe all those orders were delivered. This doesn't mean BFL can be trusted.

Hmm, but if they did deliver working products, then what's the problem?

@Pacerier: The first problem is that they delivered them a year late, when they were already worthless.

I mean if we don't pre-order new products but merely order already developed products, then there's basically no problem right?

@Pacerier: BFL are not trustworthy, if you want to do business with them it's your own risk to take.

I can understand that they are not trustworthy. But exactly what kind of risk are you talking about when we purchase their products that have already been developed? What risk is there in that?

Beyond the concerns about BL's ability to deliver, should they be successful it's very questionable what kind of return you'll be able to get as an individual user even with the substantial increases in efficiency they promise.
With Bitcoin mining, the number of coins dispensed in a given time period is fixed and self adjusting to the relative strength of the network.  When the pre-orders are all tallied and the first production run ships, we're likely going to see lots of chaos as the total network hash spikes up with each block of BL units being plugged in, but eventually it should hit some kind of equilibrium.... At which point exactly the same number of coins will be dispensed to the people who own BL hardware, relative to the $$ they invested with BL.
That said, I pre-ordered a Jalepeno yesterday.

Since you ordered the Jalapeno June 2012. Have you got it? I just ordred one 5 minutes ago. Did you have to wait 6 months before you got anything.. if you got anything at all?

BFL has not yet shipped any units other than a dev unit to luke-jr who authors the hashing software they use.  They insist, however, that they will be shipping soon.

@eMansipater, still?

I have sent Butterfly several emails inquiring about delivery dates, and etc after pre-ordering the Jalapeno.  I have yet to get a response back now 4 weeks later, I have sent them another request...this time asking for a refund.  I think they should of put a lot more info out there about how long it would take to get our orders.  I don't want my Miner next year, I want it while I will be able to actually a decent profit out of it.

I preordered 3 jalapenos. I made a calculation about the net profit with them.
If right now a ATI card of about 150 USD gives about 350MH/s and produces about 0.125 BTC/day, a new Jalapeno costs is 150 USD with 3.5GH/s, so it should produce about 1.25BTC/day, and be like having 10x ATI cards.
Maybe it will deliver a little less, because the cost of energy is lower with the Jalapeno.

Did you get them? And did you prove your calculation?

@mario did you get yours?

Playing by the rules, doing the right thing is of the utmost importance. This often times causes situations that are much harder to deal with or endure, as well more expensive. Understanding that when we buy from a company we advocate for them, through the purchase from them, we as consumers empower them to grow and proceed. It is critical that we ensure the company is something we wish to support. Though we many not always be able to do this, nor is it always possible to gain the required information, we should still try. As Americans we really need to, especially now after all we have learned from history, investigate who it is we purchase from.
Purchasing from companies that harm our workers, only harm ourselves. Supporting Wal*Mart and thousands of unhappy people working at those locations, while destroying our own economy and infrastructure is irrational. Dealing with major banks that have bad histories is another bad idea, and supporting any structure of power that does not value humanity at it's core is something I can not and will not do.
The importance is people realizing that business is to support people, and that it in it's self is a fabrication in reality and has no feelings, if it's interest is not to support people than surely it will only harm society as a whole so a few can become super inflated. I am not so disassociated with reality to think that those who have worked so hard as to earn a sweet spot do not deserve it, no sir. Merely stating that in the game of chess, both kings present are very honorable, and every piece was willing to protect them at all cost. Few companies carry compassion, honor and dignity within their model. The standards displayed by the staff at Butterfly Labs Inc, is exemplary of how a true business treats people. This (King) in modern society equates to an honorable business, whom one would want to empower and support, and thus purchase from.
I can now explain better what has happened. I contacted BFL and (assumed) competition companies, I constructed e-mails to each, much like what BFL received from me. I picked a horrible overrun time when not only is product supply low but customer service staff would be having the most difficult time dealing with unruly customers. I picked an ambitious easily discarded set of criteria to contact about and let the pieces fall where they may. Here is how it played out, and why BFL gained so much clout.
No company replied to me except BFL, not one. Granted there are only a few that can be contacted in this case. The few are very commonly known and are not easily mistaken, and the names will remain obscured for ONLY the sake that everyone makes mistakes. The information given was legitimate and NOT FABRICATED, the texts generated were by my own person.
BFL not only assisted me with finding what I was looking for, but went above and beyond the call of duty! The staff seemed happy and willing to help me, even when they really had no such obligation to such a situation I presented them with. It is in my personal opinion and within my observational reason to say that Butterfly Labs is not only a company that does care about it's customers, but one that cares about it's employees as well.
This information has been sent to the BBB © 2012 BBB of Alaska, Oregon & Western Washington (In the form of business compliment)
http://alaskaoregonwesternwashington.bbb.org/
   If at any time BFL would like to use my information gained in correspondence with me they are allowed to do so as they see fit.

WHAT, THE BUTTERFLYING ****

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
bitcoins from the future
It is likely that the Galaxy Note 2 will be launched in August.  As it has taken two weeks to mine my very first bitcoin, it seems unlikely that I will have mined enough to purchase a Note upon release (unless the time between launch and release is about 15 years).
My plan was to bank on the idea that time travel will be possible, and so I would leave a calendar entry for my future self to travel back in time and credit my bitcoin account with the necessary funds that I have mined in the future (my future self can simply snooze the calendar entry for another decade if time travel is not yet possible).
However, it occurs to me that the bitcoin protocol is immune to this type of temporal shenanigans, as any future mined bitcoins are not in the block chain and so cannot be used in contemporary transactions.  Even if the source bitcoins were already generated, no transactions would exist that showed them to be mine.
I am impressed that our future selves cannot tamper with bitcoins in the past, but I wanted to confirm that I haven't missed anything.  Is there a workaround that my future self could employ so that they didn't have to convert to gold or diamonds first (considering some time travel techniques only permit living tissue and their contents to be transferred).

Please note that the Note 2 launch is two weeks away still, and no money has magically appeared in my account as yet.  If it hasn't appeared in time, then it means either none of the answers were good enough, or far less likely, I don't discover a way to time travel back to this point to provide the BTC.  So keep coming up with the ideas :)

If time travel was possible,   it would be possible to brute force an address.  How?  Try to crack an address for 10 straight days.  Did it work? no, then go back 10 days and start off where you left off.  Repeat

Your future self could memorize some SatoshiDice secrets after they are revealed.  This would allow him to win every dice bet he placed after travelling back in time, since knowledge of a day's secret allows one to determine whether a bet will win or not before placing the bet.
There is a theory that this has already happened.

Chris, did that poster exist prior to my question?

No.  I just thought it was a funny idea.  Especially how you can quite clearly tell there used to be a 'K' between the 'C' and the arrow thing.

Heh, I like it immensely

Thanks.  :) :) :) (one smile was enough - the comment box insisted that my comment wasn't long enough)

Trying to earn money from Bitcoins from the future would not be such a lucrative business as betting on sports events, or playing the lottery. You can't spend coins that haven't been mined yet, and while you could know the exact block chain data that will appear and try selling the miners nonces that will solve their blocks, I don't think it would earn you too much. As a side note, injecting a long part of the blockchain into the Bitcoin network could freak a lot of people out - after all, they would see their money disappearing and appearing from future transactions without them authorising anything.
Knowing information from the future you could try playing on the Bitcoin exchanges, for example by buying a lot of coins soon after Bitcoin was launched for pennies and selling them at the bubble burst for $30 a coin. Moreover, you could start developing GPU or ASIC miners way in advance and be ready to blast everyone out of the water with your futuristic technology. Lastly, you could just create Bitcoin yourself and be Satoshi Nakamoto, the time traveller;).

If it was me, I'd travel back in time to when bitcoins were practically worthless and offer to buy someone a pizza in return for 10,000 BTC. That would make a nice little nest egg for the future...

You could memorize a single private key.  In the future (once time travel is invented) you wouldn't mine in the future.  Instead you would go back in time, not to the current time but back to 2009.  With your future tech mining gear you could trivially mine a significant fraction of the early bitcoins.  You may need to consult your time traveler manual to reduce the changes to the timline.  For example it likely wouldn't be a good idea to massively inflate the early difficulty and scoop up 99.999% of the coins.  You could alert the timeline and prevent Bitcoin from ever taking off.   However lets assume that mining a small portion (say 10%) of the first years blocks wouldn't be noticed.   You could direct those 262,800 BTC to the private key you memorized in 2013.   In the modified timeline you would have to do anything your wallet would "magically" produce a private key which had 262,800 BTC mined to it.  Tada, you are instantly wealthy and can buy the Galaxy Note 2.
Of course the fact that your current wallet doesn't contain 262,800 BTC means either time travel hasn't been invented in your lifetime, you for some future reason never make the attempt, or your attempt to travel back in time failed (your future self may have been assassinated by Time Police).   On the last possibility it is possible this post gives you the idea which your future self attempts to implement resulting in your death.  Of course now that you have the idea it is impossible to un-know it so your future death may be predestined.  If that is the case I sincerely apologize for getting you killed in the future.

Actually, the safe assumption is that if your approach worked, I would have the BTC right now.  As I don't your approach is flawed and so I cannot accept this answer :)

If I have a blockchain from the future I could probably go back in time and successfully perform a 51% attack.  There wouldn't be any way that I'd benefit financially as I couldn't change that blocks but I could slam a couple hours worth of blocks through.

That would be a very strange 51% attack, as it would include transactions that spend coins before people intended to spend them, as if you had the private keys to generate the transactions yourself. All hell would break loose...

You can't just copy a naturally-generated future chain because Bitcoin nodes won't accept blocks with a timestamp too far in the future.

In the future you can also buy some 'vintage' coins that would be in the blockchain in 2013 and send those to your Galaxy Note.

In the future buy private key(s) that had balances in the past.
In the past listen to a noisy data source tied to hardware random number generator.
In the future use time travel powers to alter the 'noise' your past self listened to by encoding the 'noise' with the private key(s) purchased in step 1.

You could also use your time-travel-information-channel to mine blocks, but this would limit you to 300 BTC/hr.
Happy time traveling. :)

300BTC/hr would net me enough for the phone in 1 hour, so that is fine.  But if I now have private keys that have had balance in the past, surely they collide with someone else who already has the keys?

It is true that if you steal from the private keys that it will be detected.  In a sense you are stealing from the miner as well, they just won't notice.

My future self, having invented time-travel would then send a Terminator (in the form of a CAT5/USB-toting R2D2) back in time to the beginning of Bitcoin. Not only would the "R2-Terminator" create a wallet and start mining, but would also follow programmed trading tasks to take advantage of market fluctuations. Unbeknownst to me this is all currently occurring.
Tomorrow at 9.46am GMT my modest Wallet is going to receive the culmination of R2's hard work.
Would you like some for your phone?

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text:
Will the block data saved or discarded after synchronization? Does it get removed when uninstalling?
When I first installed the program I noticed that it was synchronising with the network, and whilst it was doing so it was downloading blocks. I wanted to know if these blocks will be saved on my hard drive or will be be deleted after the synchronising is complete. If the files are stored on my hard drive I wanted to know if when I uninstall the program will the files also be deleted?

The blocks will be stored on your hard drive in the application data directory. If you uninstall, the block files will be kept. There may be an option in the uninstaller that will remove them, but the wallet.dat file will be kept for certain.
Future versions of the mainline client, Bitcoin-Qt, will handle this storage differently via Simplified Payment Verification.

Additionally, since Bitcoin Core 0.11 you enable pruning, which will delete old block data after downloading and verifying.


text:
If your wallet.dat back up is outdated, do you lose your coins since the back-up?
My last back up of wallet.dat was from the beginning of the year. My computer crashed recently and I don't have the most recent wallet.dat after receiving bitcoins. If I use my outdated wallet.dat, do I lose the new bitcoins I received?

If you made more than 100 transactions and individual receiving addresses combined, yes.
Best way to find out is to try.

To explain the '100': With standard settings bitcoin-qt keeps 100 unused addresses available at all times. Whenever an address is used, another new is generated. If you create back-ups only very irregularly, you can run the client with e.g. -keypool=10000, to have more unused addresses in your wallet, which would make your backup useful for a longer time.

Unfortunately you are right. If you run out of addresses (100 in the pool) Bitcoin-qt would have generated new addresses and those are not in that old backup, so you don't have the newly created private keys then you can't access the coins on them.
You better start using a deterministic wallet, like Electrum or Armory, if you don't have set up a good (automatic) backup process.


text:
Now that my GPU mining rig will be made obsolete, where to turn?
With the return from GPU mining likely to be affected by ASICs, where can miners turn their machines? Should I become a pro gamer? Join a rendering farm for cash (do they exist?) and let Disney use my rig to make toystory 4? Donate it to SETI@HOME or FOLDING@HOME? Donate it to an Anonymous botnet? Join a spamming farm used to bombard Bitcoin dev's with requests to switch double-SHA256 for double-MD5 in the code?
In short, what serious alternatives are their for profit or just putting to good use mining rigs?

I am interested in joining a rendering farm, can someone tell me if it actually exist?

Unfortunately, none of those other uses are worth the power your GPUs consume. I'd say sell it and use the money to find a new hobby, like skiing or flying model helicopters.

Vanity mining for example over at my Vanity Pool. Thanks to split-key vanity addresses anyone can request a vanity address without compromising their security, set their own bounty, and anyone with a mining GPU can try solving the work and claiming the bounty.

Yes I've seen this referenced but imagine it is a very small market in comparison the amount of mining resources being freed for such application. So the return on investment is questionable and probably miners are going to be looking for more options.

@gesell Well, I bet a lot of people would want to have their own vanity address, so if the pool will get popular with the miners, they might in turn spread the word to other people to use this.

Folding@home can run calculations on your GPU, Seti@home at least support nvidia.
There's also gpugrid.net, which seems to be specialized on using GPUs for medical research.

not really comparable to bitcoin and no financial return, or are they paying for cycles at these projects now?

you could mine litecoins; the advantage of having a GPU over a CPU is not as pronouced as with bitcoin but it could still be profitable. you may have to run those numbers though. ltc-charts.com for exchange rates.

heres a comparison of mining hardware https://github.com/litecoin-project/litecoin/wiki/Mining-hardware-comparison

You certainly could mine Litecoins and the return is similar to BTC


text:
Mining with a Lenovo Ideapad Y580 (GeForce GTX660M card with Optimus)
I wanted to do some mining with my IdeaPad Y580 which has a NVIDIA GeForce GTX660M and Intel HD 4000 integrated graphics, switched using Optimus. Laptop is running under Ubuntu 13.04.
The problem is i can't launch a miner (i tried cgminer and poclbm) on the laptop. I usually get the error like 'Nothing to mine on, exiting', or something similar.
The question is, how can I configure the miner/OpenCL to get this working.
Also I know that NVIDIAs/laptop graphics are ineffective in BTC mining, I just wanted to see how many Mhashes does my card get.

Got OpenCL installed?

Both the GeForce and the Intel HD 4000 should be OpenCL capable and possible to mine on.
The problem may be crippled drivers. I know HP and Dell make their "own" AMD drivers, meaning they take AMDs drivers and remove OpenCL support. Proper drivers from amd.com often refuse to install on those laptops. That's HP and Dell "helping you" by breaking your computer. Maybe Lenovo does the same with Nvidia drivers?
I would try to install the latest drivers from nvidia.com
For the Intel HD 4000 you could try getting drivers from http://www.intel.com/p/en_US/support/detect/graphics or even installing their OpenCL SDK from http://software.intel.com/en-us/vcsource/tools/opencl-sdk although I think that should not be necessary.

Oh. I forgot to say that I'm on Ubuntu 13.04, and I use drivers from the official repo.

I think you'll need proprietary drivers from nvidia.com - I believe the open source drivers don't have OpenCL support.

I am using the proprietary drivers - they come from a Ubuntu official repository.

I'd try drivers from nvidia.com

I'm getting 40mh/s on windows casual mining with bitminter client on this laptop, is that typical or additional opencl drivers will improve this?

@sonjz In 2015 if you are mining on a computer you earn less than the electricity costs, so the more you mine the more money you lose. It's also so slow that you never earn enough to cash out. Look up bitcoin ASIC mining hardware instead.

@Dr.Haribo thanks for the reply.  Yeah I started to look at the calculations, I had mistakenly thought I was getting 40GH/s, even so, after looking at the numbers again, probably not worth my while at the moment.


text:
How big would the transaction history be if all spent transactions were pruned?
If the transaction history's Merkle tree were pruned to remove all transactions that have been completely spent, what would be the size of the transaction history in comparison to its current size?  (In percent of total size.)

Note that transaction history is not stored in a tree nor is there a Merkle tree for all of the transactions in the blockchain. Merkle trees are only used for constructing the merkle root in blocks and constructing transaction inclusion proofs for SPV nodes.
If you reduce the blockchain to only the data absolutely needed for a node to verify new transactions, you end up with a node that just has the UTXO set. The state of the blockchain boils down to simply the set of all Unspent Transaction Outputs. This is because in addition to spent transactions, it is unnecessary for nodes to store transaction inputs (they are only needed for validation, so after validation, they can be discarded), other outputs in a transaction that have been spent, and transaction overhead data (such as version number and locktime).
As of block 688004, my node has a UTXO set size of approximately 4.5 GB. Note that there may be optimizations in the way this is serialized so that it is more compressed that it would be if you extracted them directly from transactions, but these optimizations should not cause a significant reduction.
Storing the UTXO set and using that for validation is actually an optimization that Bitcoin Core and some other node software do today. This enables faster validation and a more efficient way to prune the blockchain. By having the UTXO set separate from the blockchain, a pruned node can just delete the majority of previous blocks and still be able validate new transactions through the UTXO set.
Of course it is not safe to only have a node store just the UTXO set and discard all blocks after validation. If there is a blockchain reorganization, the node will need to be able to rollback the UTXO set changes made by the block being removed from the main chain. As such, it is necessary for pruned nodes to store some blocks so that it can perform this undo operation when necessary. Because blockchain reorgs tend to be short (there have not been reorgs of 2 or more blocks in a very long time) and rare, Bitcoin Core's default is to store 1 days worth of blocks.

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text:
Lottery Mining?
I know mining is extremely difficult now.
I just wondering has anyone "won" by solo mining a block? How does the chances compare against say wining the lottery?
Assume 3 Giga Hashes Per Second say.

related: Solo mining just for luck, realistic?

related: What are the odds of discovering a block as a solo miner?

Unless the lucky winner were to announce his luck, there is no way for anyone to tell the difference. So, even if one cannot find any information suggesting that someone did, it could have happened.
Blockchain.info gives the current hashing power as 47,289,554.08 GHash/s, so your chance to mine any one block would be 3/47,289,554.0 = 6.3439e-8.
In Germany there is a popular lottery where you have to guess six out of 49 and one out of ten numbers. The chance of getting all seven numbers right is 7.1511e-8. So, the probability to win the jackpot is currently as likely as solo-mining a block with 3GHash/s. Of course, the lottery has a bunch of smaller prices for getting it partially right, and the jackpot would be worth millions of Euros, not 25 BTC.
But then, it is cheaper to play "Bitcoin lottery" and the draws are more frequent.
Below an estimate of the chance to get one block out of a day's/year's worth of blocks (disregarding increasing difficulty):

Altogether, it seems to me that regular lottery is more profitable, but then "Playing lottery is a tax for people that are bad at math.".

Currently network's capacity is about 41000000 Gh/s. In this case your odds is 3/41000000=0.00000007%
For example, your odds to receive royal in hold'em flush is about 0.0002%
So good luck!

Here is a real world jackpot!
https://bitcointalk.org/index.php?topic=763510.msg13463822#msg13463822

Are these odds estimates per second or per block? In case of second, I'll look at a year is 60×60×24×365= 31536000 seconds per year
31536000x[9•10^(-6)]<238 (measured per second)
In case of block, divide by how long it takes to do a block.
No, your odds do not increase per each second - each set would re-randomize. Yes, the hash rate generally increases over time.
Like seeing a royal flush after shuffling your cards each deal, the odds stay the same per deal but would it not be an anomaly to NOT see a RF after 10,000 deals?


text:
So a computer is now called a "Miner" and is creating currency?
What I do understand:
Banks have inflated currency and through this the value of just about everything has been manipulated to make people who do next to nothing for it become rich.
What I don't understand:
How yet another "currency" will solve anything, or what Bitcoin is supposed to be solving?
How computers are creating currency that I'm supposed to trade my labour(or fruits of) to a human being who somehow claims ownership of this currency?
How to become the owner of such currency?
How the value of this currency is determined, if it came from nothing?

Taking your questions in order:

How yet another "currency" will solve anything, or what Bitcoin is supposed to be solving?

Because this is a currency that has different properties that avoid the properties of other currencies that create these problems. For example, the supply of Bitcoins is fairly precisely defined and nobody can devalue them through direct supply inflation. Nobody can discover an asteroid full of Bitcoins and increase their supply.

How computers are creating currency that I'm supposed to trade my labour(or fruits of) to a human being who somehow claims ownership of this currency?

It's the same way other decentralized currencies work. If you use, for example, gold as a currency, someone goes to the effort of mining the gold. Then they trade that gold for other goods and services they need to continue mining. Others trade goods and services for the mined gold. With Bitcoin, computation work is needed to secure the transactions, miners get newly-created currency in exchange for this service. You have to distribute a decentralized currency somehow.

How to become the owner of such currency?

Buy it on the open market. There are many sites where you can buy Bitcoins. You can't really mine Bitcoins at a profit easily -- if you could, then the number of miners will increase and they'll each get smaller shares. This will tend to keep mining just barely profitable, for those who do it well, over the long term.

How the value of this currency is determined, if it came from nothing?

The same way as the value for anything else is determined, supply and demand. It's value is whatever price buyers and sellers meet at.

(Answering in order):

Bitcoin is a currency defined by a consensus of the people. Bitcoin takes money out of the hands of bureaucrats and into the hands of the people.
Mined bitcoins are the start of their life. The miner will most likely sell them for power and more mining equipment (probably with a exchange to fiat in there).
Same way as USD. Do jobs, get currency.
The value of a bitcoin is determined by those who trade it. Exchanges like Bitstamp and Mt. Gox are a somewhat centralized way of defining a value of a bitcoin to fiat, which in turn can be used as the fiat <-> item value.


text:
Is there a site (or formula) that easily calculates returns using difficulty / hash rate?
I'm just a novelty miner, looking to be cool and do my part to decentralize. Not looking for a return on my investment.
However if I'm going to spend $100 or so I'd like to calculate how my options will fare. Any sites that have no affiliation to hardware, just calculate returns on current difficulty & a hash rate that I specify?

Have a look at coinwarz.com - it list's alot of crypto currencies, difficulty and includes a calculator to measure ROI when considering mining.


text:
Is there a correct way to refer to "orphan" blocks?
I was reading a passage on the bitcoin wiki that pointed out that it doesn't make sense to call invalid chains "orphans," since, by definition, every block in the blockchain except the genesis block has a parent.

Blocks in shorter chains (or invalid chains) are not used for anything. When the bitcoin client switches to another, longer chain, all valid transactions of the blocks inside the shorter chain are re-added to the pool of queued transactions and will be included in another block. The reward for the blocks on the shorter chain will not be present in the longest chain, so they will be practically lost, which is why a network-enforced 100-block maturation time for generations exists.
These blocks on the shorter chains are often called "orphan" blocks. This is because the generation transactions do not have a parent block in the longest chain, so these generation transactions show up as orphan in the listtransactions RPC call. Several pools have misinterpreted these messages and started calling their blocks "orphans". In reality, these blocks have a parent block, and might even have children.

Is there a better way to refer to these blocks?

Perhaps we could call them 'disowned' blocks, since they're no longer the favored child of their parents. /s

related: What are orphaned and stale blocks?

Pieter Wuille suggests extinct blocks:

The first is perhaps best called extinct blocks. These are blocks that were produced by building on an block that is no longer the active tip of the chain. Some nodes may have considered it to be the best block at some point, but they switched to another chain which does not contain the relevant block anymore. They are valid, verified, and their ancestry up to the genesis block is fully known - they're just not currently 'active'. They are sometimes called stale blocks (typically in the context of mining software realizing it built on old data) or orphan blocks. The latter name [orphans] originates from the fact that payouts from extinct blocks are denoted as "orphaned" in the reference client (referring to the fact that their coinbase transactions are now orphaned).


text:
Can Bitcoin be used in QuickBooks?
I'm wondering if I can manage my bitcoins with my other securities? Or incorporate them into a business plan.

Sure you could However it would be necessary to know how you transact with the coins...do you simply trade them out for fiat immediately?  If so, then I would create the payment as a check from the exchange for the dollar equivalent that was collected and put the transaction ID and recipient address in QB.  You should probably setup something like coinpunk or at least a full wallet server so that you can issue one time use addresses that are meant to be tied to your customer's account.  This way, it will be easier to reconcile later.  If you try to process your payments together manually into your own wallet, then I at least suggest to create a new wallet each month so that your transactions can be bundled together for ease of reconciliation purposes.
I don't think that you can add XBT as a currency yet within QB but then again I haven't used it in a couple years now.

I ran across this recently (http://www.qbgarage.com/multicurrency/), you CAN use multiple currencies in Quickbooks, but it is a permanent change that adds complexity to your books forever. There is also the ability to add custom currency definitions (like XBT), but these must be updated with market prices manually, until QB supports XBC on their price service (or someone writes a script or something.)
I like the above answer the best if it fits how you use bitcoin. If you need more, go for it, but don't overdo it.

FWIW that may happen sooner than you think.  I have ties to an Intuit Senior Strategist and would be willing to make the push for it if you could give me links to forums where other QB users are itnerested in utilizing Xbt currency.

You can use Bitpay now for some quickbooks transactions. Their software will allow you to track all of your transactions, which can obviously be quite helpful for any business accepting Bitcoins.
If you have questions about this, you should check out Bitpay. As I understand they've actually set up a separate help desk just to help Bitcoin users.
Bitpay is a highly reputable company based in the US and it's backed by Silicon Valley venture capital, just in case you're wondering.


text:
Trying to open directly...Device open failed
Ubuntu 13.10 & amd-catalyst-13.4-linux-x86.x86_64.zip
xorg.conf created by
# aticonfig --initial -f --adapter=all

Thereafter, i modify it with next /etc/X11/xorg.conf
Section "Module"
        Disable        "dri"
        Disable        "dri2"
EndSection

Start phoenix:
$ ./phoenix.py bitcoin_deepbit_gpu.cfg
[10/28/2013 02:30:08] Welcome to Phoenix v2.0.0
[0 Khash/s] [0 Accepted] [0 Rejected] [DISCONNECTED]X server found. dri2 connection failed!
Trying to open directly...Device open failed

Start cgminer:
$ ./cgminer --scrypt  -T --url stratum+tcp://stratum.coinex.pw:9000 --user user --pass pass --no-submit-stale --queue 4 --scan-time 1
 [2013-10-28 02:41:21] Started cgminer 3.6.6
X server found. dri2 connection failed!
Trying to open directly...Device open failed

I have partially solve this trouble with --gpu-platform 0:
$ ./cgminer --scrypt --gpu-platform 0 -T --url stratum+tcp://stratum.coinex.pw:9000 --user user --pass pass --no-submit-stale --queue 4 --scan-time 1
 [2013-10-28 02:43:12] Started cgminer 3.6.6
 [2013-10-28 02:43:12] Probing for an alive pool
 [2013-10-28 02:43:17] Pool 0 difficulty changed to 64
 [2013-10-28 02:43:17] Network diff set to 0
 [2013-10-28 02:43:17] Stratum from pool 0 detected new block
 [2013-10-28 02:43:19] Found block for pool 0!
 [2013-10-28 02:43:21] Found block for pool 0!
(5s):7.156K (avg):18.36Kh/s | A:0  R:0  HW:0  WU:35.4/m
....

But what is it?
Trying to open directly...Device open failed
Why does it trying to open device disabled by module directive in the xorg.conf?
And how to specify platform for phoenix miner?
There is only one option in phoenix config:
name = GPU 0 #The name to display the device as (default is device ID if not specified)

It doesn't help.

Could you please clarify what exactly your question us?

Check, I'm trying to clarify it for you.


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Why did Dogecoin fork into 3 chains and not just 2?
This I never understood ever since Dogecoin forked in mid-February 2014: If the cause of the fork was, apparently, the same as the one that affected Bitcoin in March 2013 (namely: a very long block being accepted by a new wallet using a different database but rejected by the earlier wallets) then...
How come there were up to three forks of he blockchain at a time? I would've expect at most 2 competing chains, one kept forth by the miners using the old version (then, 1.4) and another by those already on the new one (1.5, then). But, how was it possible to have three forks?
And finally (rant here), what was the point of increasing the size of the potential block size? In retrospect it's obvious something like this was going to happen. Why not treat the rules of a coin as set in stone once it's released, non-critical bugs and all? I had to delete the blockchain and resync twice, each time getting into a different, invalid forked chain - at the end I simply downloaded the files a volunteer shibe uploaded, with the potential risks that has - and hated the experience.

The articles you link attribute the forks due to raising the total coins limit. Which changed from 500 million to 10 billion. Now this by itself won't cause a block chain to fork, until there is a transaction larger than how many coins there should exist according to old and outdated clients. In Dogecoin's case someone created a 500+ million transaction that would create an invalid block from an old node's perspective.
To create multiple forks, you'd simply stem from newer blocks in the "outdated client" chain. Old clients would reject it and opt for blocks created by outdated miners and newer clients would be hit by a self inflicted 51% attack of sorts. Where newer nodes have multiple chains to sort and make a decision on. As an example here are the chains a newer updated node would have to choose from.

Original client chain
Original client chain with leading block containing one 500+ million transaction
Original chain with second-last block containing 500+ million transaction

It goes with the longest chain initially, but what happens if another chains mines a few blocks faster and becomes the leading chain? It switches over, and you have this complex multi chain scenario.
Why was the total coins possible limit increased?
The creator simply didn't expect this, all though it is really expectable. Dogecoin was set to mine itself out entirely within 1.5 years from release. Compare this to Bitcoin's ~2 centuries from now. Whoever configured these initial values expected Dogecoin to become irrelevant within this time frame or simply wanted cosmetically large block rewards to entice people.

I don't understand how that would allow for a third fork: Old clients would prefer the longest chain without bigger blocks, while the newer version clients would consolidate to the longest chain in total, hence one should only have two forks?

Understood it as: old chain is kept sans the 500+ trans. by the old-client miners, both miners see this chain as valid. Chain with 500+ trans. (new miners' only) gets worked on by some of the new-client miners, others try to add this trans. to the oldies' chain, resulting in 3rd chain. Between 2nd and 3rd chains only one should prevail, except some new miners continuously try to add offending trans. to the oldies-only chain at diff. points, spawning new forks that compete for new-client miners' attention.

@Murch imagine that hash rate is split some what proportionally, meaning any chain could momentarily be the longest.

No problem with temporary chains, but under the light of Joe Pineda's question specifically asking how three forks could exist in parallel, I thought you were suggesting that there could be more than two stable forks.


text:
ASUS X1650 256 MiB - is it sufficient?
Just learned about BitCoin. As I learned now there is no sense using CPU, just GPU. I have ASUS X1650 256 MiB, is it sufficient to ear at list 1-2 BitCoin a week?

I suspect not - it's getting really hard to make money as a GPU miner, unless you managed to get an AMD card for cheap. Also, the amount of video memory doesn't really matter.

no, GPU mining going to become obsolete sooner or later. If you have money buy bitcoins from a exchange / trader, otherwise you can preorder / wait for ASIC miners.

To be honest, no. I have a 5770 and I get 200MH/s; not really worth it unless you look at it as a hobby and don't want big returns.

200Hms - it's how many coins your mine a week?

@ManInTheHood I suspect that Dominic meant 200 mega hashes per second. To figure out how many bitcoins that is, look here. Right now, that's about 1 coin a month.

No. That card is WAYYYYYYYY too old. It wasn't good when it was new, and this isn't 2007 anymore. Doesn't have the technical specs required. period. No chance at all to make ANY money. not even 1 cent. Even with a proper video card, i am only making 8 cents a day after power costs (about 1.87 revenue and 1.79 in power costs).
Go here for the profitability calculator. http://www.bitcoinx.com/profit/
And as far as Hash rate (MHash/s) goes, remove 60,000 and put in 1 because 1 is all that card is going to get and that is a long shot.

Abei, I think your numbers are off. I get 3 MHash/s with my i5 750, and that's a CPU.


text:
Does bitcoin improve on "hard" currencies in any way?
Question is in the title. Anyone who's toyed sufficiently long enough on the foreign exchange understands that currencies are largely driven by sentiment or manipulated on the odd occasion. Plus, there's the fact that money has no intrinsic value. Has bitcoin overcome any shortfalls and risks of conventional currencies ?

When you wrote "money has no intrinsic value", did you mean fiat money, or bitcoin, or what?

Fiat money or legal tender. That's the way it's described on investopedia. The inconvenience this could cause according to my understanding is that money can lose a lot of it's value in the event of a substantial crash. Hence the interest in gold at the moment.

possible duplicate of What are the perceived advantages of bitcoin as a store of value?

This question is a pretty much a dup of my previous comment and http://bitcoin.stackexchange.com/questions/305/what-are-the-perceived-advantages-of-bitcoin-as-a-means-of-exchange

There are huge differences between FIAT and Bitcoin.
Fiat is created out of thin air "with fractional reserve banking" and other mechanisms, there is no stop on how many will be created.
Another problem is that every country is FORCED to create more of it.
Since otherwise the value of their money would increase to much, ending all export industry and tourism in that country.
So when the US prints an extreme amounts of FIAT they know that China must follow, which means that Japan must follow and the US must print more, and so it goes on.
Bitcoin can not be created out of thin air, and it takes an ever increasing energy cost to create one.
And since no country base their economy on it, its free from having to be endlessly printed. (It can´t even if it would be.)
Another very important difference is that Bitcoin is the only digital money you can own yourself with no one else having any access, and thus keep on your own computer or in your own cellphone or store on a USB the key to your money.
All other digital money, is money that is stuck in a bank and thus they might play around with it and go bankrupt.
But a Bitcoin is a Bitcoin and not simply a promise in their system.
This also means that you can send them any time of the day instantly to anyone you like now even on Facebook or in emails.
The limited amount also gives it a longterm backing in that if it picks up in any market, it cant stay this low and will have to go much much higher, a value of something like $50-$5000 would not be strange in 10-20 years IMO.

"Bitcoin can not be created out of thin air." That is not true. Please see: http://bitcoin.stackexchange.com/questions/8776/could-there-be-hyperinflation-in-bitcoin

There are some important shortfalls of traditional currency that Bitcoin addresses:

There can never be more than 21m bitcoins in existence. Bitcoin will never be vulnerable to the quantitative easing or printing of additional currency which devalues the existing funds of holders of traditional currency.
There is no central authority. A collapse of any particular corporation or govt will not cause Bitcoin to fail. There's no need to participate in a run on a bank.
Bitcoins are very difficult to steal without coercion when protected in the right way. Security features for Bitcoin are still maturing, but it is possible to encrypt a Bitcoin wallet on an offline computer and do transactions from there. This heavily reduces the change of bitcoins being stolen through malware or physical theft of hardware.
Bitcoins can be spent over the internet with very low transaction fees (a fraction of a percent compared with 3-4% with a credit card). When you know an internet retailer is trustworthy, Bitcoin is a great way to make payment.
Transactions are essentially irreversible.
Bitcoins cannot be counterfeited.

Though Bitcoin is obviously subject to manipulation through trading on exchanges, this has little effect on its usefulness as an online payment method as they can readily be converted to another currency before fluctuations have much effect.

Point 3 is horribly misleading, please remove it, especially since the rest of the answer is quite true.

@Lohoris, would you be happy if I reworded it to say they are "difficult to steal"? I'm not quite sure what's misleading about it, except maybe that I should add that the level of required technical computer knowledge to prevent theft is currently very high? The point I was getting at is this: someone can steal your computer, steal your wallet, burn down your house, get your bank accounts cancelled, but provided you have a copy of your encrypted wallet somewhere, you've still got your bitcoins.

http://xkcd.com/538/

@Lohoris, I've updated it... thanks for the feedback

Bitcoin as a currency is being inflated, currently, at a rate of 28% per year.  That alone would disqualify it as being one of the "hard" currencies (i.e., United States dollar, Euro, Swiss franc, British pound sterling, Japanese yen) for a long time to come.
Bitcoin most definitely is driven by sentiment and with the aggregate of all order books being slim, it can likely be manipulated up or down with simply a six figure budget.
Where bitcoin's primary advantage comes into play is that the currency inflation rate a year out, two years out and ten years out is already known, today.
Additionally, when trading currency there is no T+2 settlement.  Most Bitcoin exchanges settle trades instantly, and deliver bitcoin withdrawals in seconds.  Thus the funds can then be used for spending or further transfer just minutes after the trade executes.
Unfortunately, the bitcoin exchanges are not as great with the flow of fiat used for trading.  Arbitrage would keep the exchange rates about even (less trading costs) however because fiat funds don't flow cheaply or quickly in and out of the Bitcoin exchanges, exchange rates between exchanges will not be consistent.
This presents an opportunity to some, but serves as a hurdle to others. Because bitcoins are not traded yet alongside other currencies for forex or are yet considered by established financial trading firms, there are first-mover advantages being enjoyed by entrepreneurial endeavors writing custom trading bots.
One other benefit is that Bitcoin is just a protocol and data, which means it is universal.  Central banks don't need foreign exchange reserves with bitcoin nor swap agreements to trade against bitcoin.  There is simply self-interested individuals and companies doing the buying and selling (for both commerce and speculation).
Here are some other benefits:

http://bitcoinmedia.com/bulleted-advantages

The Bitcoin currency inflation rate cannot be known today. For example, currency inflation rate includes demand deposits, and there is no way you can know what the total future Bitcoin demand deposits will be at any given time. All you can know is the amount of narrow money (M0) which is not sufficient to predict currency inflation. It is quite probable that many online wallet services are already fractional reserve banks whose reserve ratios are unknown, so we already have no solid idea what the currency inflation rate is.

@DavidSchwartz, in general, I agree with your comment. However, I would argue that when you use an online wallet service using a fractional reserve system, you no longer have bitcoins. Instead, you have something more like Disney Dollars, or Bitcoin E-wallet Account Credits, which don't have the same properties as bitoins. I could say the same thing about most banks using fractional reserves when it comes to govt currencies, but at least in those cases the govt is likely to cough up when the bank goes belly up.

@HighlyIrregular: It doesn't matter whether you have bitcoins or not. What matters is whether it affects the currency inflation rate. By "Bitcoin demand deposits" I just mean demand deposits denominated in Bitcoin amounts. And actually, you've brought up another point -- if a bank goes belly up, effective currency disappears. This unpredictably reduces the inflation rate. (Believe it or not, all this is actually an advantage of Bitcoins. Inability for supply to adjust to demand is bad, not good.)

@DavidSchwartz, I've just asked a related question: http://bitcoin.stackexchange.com/questions/4169/how-can-i-find-out-if-an-e-wallet-service-uses-a-fractional-reserve-system

The value of money is that it makes exchanging and storing value more efficient. Your assumption that it should somehow have other value besides that is wrong.
Bitcoin improves over traditional currencies in several ways, for example:

Easy to send payments internationally without fees.
No chargebacks.
International, no need to make currency conversion.
Easy to get started with receiving bitcoins.
Possibility of microtransactions.
No inflation.
No single point of failure.
Payment is done via digital signatures rather than giving away your password.
Objective public record of payments made in case of disputes.
An option for small countries without a viable currency of their own.
No need to rely on financial institutes with poor service.
A powerful scripting language that allows more advanced transactions than "A is paying X to B", and derivatives of the technology such as Namecoin.
Privacy.
No restrictions on whom you can pay.

Thank you for detailing the differences. About value, see my comment up top.

The idea that Bitcoin is superior to government-issued fiat is based on a few myths.
Myth #1: Bitcoin cannot be created "out of thin air"
This is not true. More coins can be created if a significant number of users (either the economic majority or the majority of the mining hash power) decide that it's good for the system. Given the history of all money, it is almost guaranteed that this will happen. It is the same as government-issued paper. Remember, the US dollar was once linked to gold, and apparently could not be created out of thin air. When rules are made by humans, the rules can be changed.
A separate but related point: nothing prevents Bitcoin from being levered like fractional reserve banking. See how gold ETFs work. Gold cannot be created out of thin air (even if everyone agrees!), but you can create paper on top of it.
Myth #2: Bitcoin is decentralized and not controlled by any single authority
Again, this is not true. Bitcoin does have an informal system of governance. A few people do make decisions on behalf of everyone else. This is just like a democratically elected government, except that it isn't democratically elected (so it's a "benevolent dictatorship"). It's very much like a central bank that decides which banks are bailed out and which banks are allowed to fail (see: 2008 financial crisis), who gets to keep their money and who loses theirs.
It's easier for the miners to tax your bitcoins than it is for the government to tax your dollars (see: Cyprus depositor tax).
Myth #3: Bitcoin cannot be counterfeited
It is trivial for anyone to create an implementation of the Bitcoin design (PDF) and call it "Bitcoin." For example, you could create an alternative version of the design with a upper limit of 42 million coins instead of the current 21 million, with faster transaction processing. Incidentally, this is exactly what Litecoin does. Litecoin could just call itself "Bitcoin" and it would be legitimate, because it does follow exactly the design laid out in the Bitcoin white paper. Therefore any number of Bitcoin clones can legitimately call themselves "Bitcoin" as long as they follow the white paper (this is how it's supposed to work), and therefore in a sense there can be any amount of "counterfeit" Bitcoin currency in circulation.
If you had an agreement with someone to pay you in bitcoins for a service you provided them, and they paid you in "counterfeit" bitcoins (which are as real as yours), there would be a dispute that would have to be settled in court. This is why Bitcoin is a caveat emptor system.
On the other hand, if you paid someone in bitcoins and they claimed them as fake, you couldn't prove it, because they could legitimately claim to have expected to receive a different kind of bitcoins. In this case you would lose your money and get nothing for it in return.

I encourage the reader to think for themselves as to the reasons for my answer being downvoted. Are the above myths not myths? Is Bitcoin any different than any other government-issued fiat with respect to the above facts? Please think for yourself. Question: "Does bitcoin improve on 'hard' currencies in any way?" Answer: no.

Correct on #1 (since e-wallets could easily do fractional reserve banking, thus "creating" money out of thin air) and #2 (for the good or the bad, majority rules - even if they implement a "Robin Hood tax"). Definitely wrong on #3: there's no way in heaven or hell that I could rob you by paying in Lite/Prime/PPC/What-not-coins if you're waiting for the payment to be done in Bitcoins - the chains are waaay too different, a transaction happening in one of the alt-coins has a zero chance of being accepted at the other chains. Nil, zero, never gonna happen.

And, anyway, you're just debunking some commonly-cited-yet-untrue myths about Bitcoin and arguing thence that bitcoin doesn't improve on currencies in any way - sorry, your logic's deeply flawed. Rosenfeld's answer addresses some good points at which crypto-coins are inherently superior to traditional currencies. To counter, you could've mentioned ways in which they're inferior and then try to argument why the cons weigh more than the pros and then you would've gotten a point.


text:
Is the price of BTC transactions driven down by the influx of miners?
I'm wondering why Bitcoin transaction speed doesn't increase (and cost decrease) due to more people becoming miners all the time. Is it because the number of transactions is increasing even faster?

No, it is because those are unrelated values. The number of miners (more preciselly the cumulative hash power) influences the security of the network, but not the speed of mining the blocks (in long term). In short term (within the current window of 2016 blocks), it can influence the block generation speed, but after the window completes, difficulty retarget happens, so that the block generation speed goes back to designed avg. time of 10 minutes.
The transactions can not be confirmed faster than blocks are generated, thus block generating speed is very closely related with transaction [confirmation] speed.
Transaction speed is also influenced by number of transactions waiting to be confirmed, but that again is unrelated to number of miners.
Similarly the price is more or less unrelated (assuming enough miners to avoid monopoly). The price (per byte of serialized transaction) is mostly affected by the demand - i.e. the number of other transactions waiting for confirmation and their size and fee used and some other subtle properties.

So, it's essentially because of the feedback-loop mechanisms in Bitcoin's design?

I'm not sure I understand your question. But for the original question, it is because those are unrelated things. Basically we have a new block created every 10 minutes and such a block is limited in its size, therefore every 10 minutes we can confirm only limited number of transactions. Before a block is mined, you can't confirm any transaction, and then it depends on whether your transaction was included in a block or not.

The difficulty of finding new blocks is set by a feedback control loop. Every 2016 blocks, the difficulty resets to the value that would have caused the past 2016 blocks to have taken 14 days. This translates to a block interval target of ten minutes. Thus, when more mining power enters the system, it only briefly decreases the block interval until difficulty adjusts to the new level of mining power. Vice versa, when the price dropped earlier this year and a lot of mining power left the system, mining became easier to speed up blocks.
This means that the transaction capacity remains almost constant since Bitcoin blocks have a fixed upper limit. Each block can confirm about 4,000 transactions (at an average of roughly 500 bytes). However, there were some capacity gains resulting from more efficient use of blockchain space, e.g. by a higher portion of segwit transactions, use of batching, better use of non-peak times to consolidate funds, and budding use of second layer technologies.
So, generally, the expected time until your transaction is confirmed is ten minutes if your transactions is among the ones that will be included in the next block, otherwise longer.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the "best" BitCoin alternative? Especially from the pov of mining
Namecoin, Devcoin, Litecoin, Liquidcoin, Solidcoin, I0coin, Ixcoin... Which of them is the best alternative to BitCoin, especially from a fledgling miner's pov (ie. I'd like to mine some coins, but have hw with very limitied abilities to do it)?
Apart from "ease of mining" - both in regards of difficulty and the blocks/timeunit - other concerns to concider may be:
-Exchange-rate (to USD or BitCoins)
-Deployment (are there actually anybody using it, is it accepted for payment somewhere)

Please don't abbreviate too much in your questions. Moreover, I think that this question does not follow the question guidelines - it should have some time frame for analysis, otherwise the answer can change over time.

Hi Baard! This question is way too vague. For this question to be answerable objectively you would have to clearly define "best". Are you looking for the one that would be most profitable for mining (including the hardware investment)? Even that changes a lot over a relatively short period of time so it's not a good question for StackExchange. I'll close this question if it isn't heavily improved soon.

Probably the best alternative to Bitcoin would be gold. It`s fairly popular, valuable and finding some small amounts for a beginning miner should be fairly easy in some parts. It would probably require you to move closer to some rivers though...
All joking aside, you should look into using some mining pool with an option of merged mining. If mining some AltCoin would be more profitable than Bitcoin, a lot of people would switch by now and drive the price down.
You could also look into using your mining power in alternative ways. I'm assuming you have a GPU mining rig. In that case, you can look into such things as mining vanity addresses for Bitcoins (for example using my Vanity Pool).
All in all, Bitcoin is probably the main way to go nowadays, so you should concentrate on that.


text:
Calculating average number of hashes tried before hitting a valid block
I'm toying with the idea of starting to mine, and was wondering how to calculate how many hashes on average must be tried before one will "hit" a valid block?  I'm talking about a single user (not a pool) using one rig.

I rephrased the question to make it general instead of specific to the current point in time, to make it more useful for future visitors.

Well, currently the difficulty is 2,440,643.  There will be (difficulty * 2^32) (roughly) hashes per block.
So that means there are (2,440,643 * 2^32) hashes that must occur before one block is solved.  That's is across the entire network.
A block is solved in ten minutes (on average) or 600 seconds.
So the network is hashing (2,440,643 * 2^32) / 600  ~= 17 Thash/s.  (This calculation is performed and the result is displayed on BitcoinWatch.com)
Let's say your dual 5970 rig gets 1.4 Ghash/s.  That is 17,770 Ghash/s / 1.4 Ghash/s = 12,693.  That is the number of rigs, if all were exactly like yours, operating today.
So if 12,693 rigs can do the work in 10 minutes, one solo rig will tka 12,693 * 10 minutes, or 126,930 minutes.    With 1,440 minutes in a day, that means it will be about 88 days before you will have a 50% chance of solving a block operating solo.
Now that was the long way.
The short way:

http://tpbitcalc.appspot.com/

For Hash Rate, plunk in 1400 (1.4 Ghash/s) and click Calculate.
So then, how many hashes is that?  There are 86,400 seconds in a day and you have to has for 88 days.  86,400 * 88 = 7,603,200 seconds.  At 1.4 Ghash/s X 7,603,200 seconds means you hashed 10,644 Thashes.
That is: 10,644,000,000,000,000 hashes.

Since it takes the network 2^32 * difficulty hashes to find a block on average, it will also take you 2^32 * difficulty hashes to find a block on average, roughly. So you can take the current difficulty, multiply by about 4.3 billion, and that's how many hashes you will need, on average, to find one block. (Assuming the difficulty doesn't change on you.)

If you are solo mining, hashes mean nothing. Whether you have a 19t/h rig or a 1m/h rig, both have the same chance of finding the correct hash to solve a block. Pool mining, true, the higher your hash rate, the better.  Solo mining, hash rate is not relevant.

This is completely false. The higher your hashrate is, the higher the probability of finding a winning block per unit of time.


text:
ATI GPU for mining with display attached to integrated graphics?
I'm running Ubuntu 12.04 and I'd like to attach my monitor to the onboard Intel graphic and have my GPU (ATI 67xx) for mining solely.
So far I'm struggling with setting up the ATI GPU. Do I need to run 2 XServers? Or 2 displays with one XServer?
Did anyone get a setup like this to work?


text:
Is there any way to install a GPU miner on ubuntu without using the proprietary drivers?
The question pretty much says it all. Any way to install a GPU miner (ATI) without
A) Installing fglrx (which is a very bad driver for everyday use, and breaks my dual-monitor setup)
B) Installing stream app sdk (which, if I understand correctly, requires fglrx)
Please? Anyway? I would like to start mining bitcoins...

No there is not. The ATI Catalyst driver implements OpenCL, which is what GPU miners use to accelerate the SHA256 hashing used in mining. The open source driver does not implement OpenCL. There are experimental projects that aim to implement OpenCL in the open source driver (Clover is an example) - as a Gallium3D state tracker - but so far these only run on the CPU.
GPU drivers are very complex pieces of software. Even if an open source implementation of OpenCL, that runs on the GPU, were to become available, it would likely be orders of magnitude slower than ATI's proprietary implementation, which basically undermines the whole purpose of using the GPU in the first place -- to gain speed.


text:
What are the odds of discovering a block as a solo miner?
I understand that during mining, one does not discover individual coins, but rather blocks of coins, and I heard that one block equals many coins (but how many?). I am wondering though, as a solo miner, what are the odds of discovering a new block? I guess this depends on my hardware but if we say that a GPU is 10 times faster than a CPU, and a $10 USB ASIC device is 1000 times faster than a CPU, and a $300 mining box is 5000 times faster than a CPU, perhaps one can adjust the odds estimations to reflect that.
Also, how many BTC would I obtain if I discovered a block?
This website http://blockexplorer.com/ seems to how a variable number.
But it seems a bit like winning a lottery.

It is hard to calculate that, as bitcoins are less and less discovered over time. Answer depends on time period of mining.

When I signed up for btcguild today, I found that blocks were frequently being discovered. One every few minutes. But they have zillions of hashes per second going on.

Related question: http://bitcoin.stackexchange.com/questions/16687/solo-mining-just-for-luck-realistic

Take the total network Th/s and divide by your total Th/s. That tells you on average how many blocks will occur before you get one.
So if there is currently 3,666 Th/s on the network, and you have a 0.55 Th/s (like you would if you have a $5,000 KNCMiner Jupiter ASIC), then 3,666/0.55 = 6,665.
That means you have 1/6,665ths of total hashing capacity. There will be 6,665 blocks before you get one.
So if there are 144 blocks in a day, then you need to wait 46.28 days to get a block when mining solo with that hardware. But that is assuming difficulty doesn't rise. With a rising difficulty you would end up waiting much longer, and possibly never end up getting a block when solo mining.
That's why solo mining is not as profitable as using a pool for anyone without tens of Th/s nowadays.

Or in the case of a USB miner, which mines maybe 5 GH/s, it would be 4600 days or 12.5 years. And with a CPU miner the chances are 1000 times worse, i.e. infitesimal. So really without good hardware this is like playing the lottery.

note that the p of {finding a block in X blocks when your chance of mining a block in one unit of time is 1/x} = (1-(6664/6665)^6665) is about .632, so you would actually only need to be mining for about 4605 blocks with .5 probability. Now that the difficulty is about 600 times harder, this is probably a moot point.

To answer your question of:

how many BTC would I obtain if I discovered a block?

25 BTC in a single block currently. This will change over time as less and less BTC are available to mine
Here is an excerpt from bitcoin wiki:

How are new bitcoins created?
New bitcoins are generated by the network through the process of "mining". In a process that is similar to a continuous raffle draw, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new block). Creating a block is a proof of work with a difficulty that varies with the overall strength of the network. The reward for solving a block is automatically adjusted so that, ideally, every four years of operation of the Bitcoin network, half the amount of bitcoins created in the prior 4 years are created. A maximum of 10,499,889.80231183 bitcoins were created in the first 4 (approx.) years from January 2009 to November 2012. Every four years thereafter this amount halves, so it should be 5,250,000 over years 4-8, 2,625,000 over years 8-12, and so on. Thus, the total number of bitcoins in existence can never exceed 20,999,839.77085749 and counting. See Controlled Currency Supply.
Blocks are mined every 10 minutes, on average and for the first four years (210,000 blocks) each block included 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks.

This is a great place to start reading about bitcoins (coindesk)

To answer you question about what is the reward for mining a valid block. Currently 25 BTC, previously it was 50 BTC until block number 210,000 was mined. The current amount will be divided by 2 when block number 420,000 is mined.
That said the fluctuation in amounts you see on mined blocks is the transaction fees. When people send bitcoin they have choice to include a mining fee (to get better chance of getting in next block faster than other transactions). Depending on the transactions your miner decide to include you will get more or less bitcoin plus the base reward of 25 BTC. So normally miners that wants to cut a profit will favorite transaction with bigger fee.

The difficulty changing won't preclude you from finding a block. However because it's essentially random, there's a chance you might never find a block, and also a chance you could find one on the first hash. There's even a chance you could find 10 in a row. It's random, like flipping a fair coin. Each try is also independent, also like flipping a coin. Just because you've flipped the coin 10/ times and it comes up tails, doesn't mean your "due" for it to come up heads. It's still 50/50.


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Can bitcoind still do CPU-based mining or was that feature removed?
I'm seeing conflicting claims about whether  bitcoind can still do CPU-based mining. As far back as 2011 people were saying that feature was going to "soon" be removed. Was mining removed?
By the way if mining is removed from bitcoind, what are the things it can still do?

It is still there as of version 0.8.5, but just a reference implementation. It's not optimized, doesn't support pooled mining, and is not exposed via the Qt GUI.
To enable, start with the -gen option. But other than testnet (and even there...), it's utterly pointless.

Is there a miner that supports pooled mining that still uses the CPU? It appears cgminer will not, nor bfgminer.

I'm mining at about 2 Gh/s at testnet using setgenerate true 1 the last number is how many cores to use, you can check your hashrate with hashespersec

@Jonas What is testnet? Where is hashespersec?

If you want to try experimenting you should not do it with real bitcoins, thats where testnet comes in. bitcoind -testnet it will create a "testnet3" folder, and will not overwrite your "mainnet" files :-)

By the way I am periodically getting "error: no response from server". I run "bitcoind -gen &" and then a while later "bitcoind getinfo" and I get this error. Any idea what causes it?

OK when I run "bitcoind -testnet" and try to getinfo, the error changes to: "error: couldn't connect to server".

I am running Bitcoin-QT, and enter the commands in the console. Not sure if this answer is up to date http://bitcoin.stackexchange.com/questions/5841/bitcoind-getmininginfo-says-hashespersec-is-0

If your running linux try ps aux | grep bitcoind that will give you a list of any bitcoind processes

@JonasOestman Pretty sure that's 2 Mh/s.

OK, it appears my config file had something in it that was messing things up. I reverted to just rpcuser/pass and now it works. However "bitcoind gethashespersec" is returning a value of 0 when I'm running "bitcoin-qt --server". However when I run "bitcoind -gen &" and then gethashespersec I do get 1931863.

But my question is still not entirely answered. If I run "bitcoind -gen" without testnet, am I actually able to generate bitcoins (even if very slowly), which will end up in my wallet.dat?

If you find a block (which, with a decent desktop CPU, at the current difficulty, would happen once every ~10000 years), you'll get 25 BTC in your wallet. If you don't, nothing will happen except higher electricity bill, and wear and tear on your computer.

@Friendly: bfgminer does support it, though you may have to compile from source.  There is a note that the cpu mining support is disabled in some of the binary distributions.

Update: The -gen option for mining was removed in version 0.13.0

As of version 0.13.0, CPU mining has been removed from Bitcoin Core.
Since which version the mining functionality removed from wallet?

Here's the release note with the corresponding section: Bitcoin Core 0.13.0 removed the internal mining capability


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Can the Block Erupter be used for anything besides coin mining?
Did the creators of the Block Erupter USB device have the foresight to make it capable of any other function besides mining coins?
I'd hate to think that now that Bitcoin is becoming impossible to mine efficiently, these are going to end up on the heap of truly useless technology.
Y'know?
Or perhaps is it still useful to mine non-Bitcoin coins?

They'll be useless.
But the name pretty much says it all: Application Specific Integrated Circuit.
That's why FPGA's (field-programmable gate array) were such a huge success. You'd have a circuit that you could program! While much slower the possibilities are practically endless.


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In bfgminer, what does Accepted mean?
While mining with a pool,
I recently noticed among the numerous "Stratum from pool 0 requested" lines that
bfgminer prints,   one saying
 Accepted (hex number) CPU 2 Diff 288/2

Does this mean that I found a valid block? Or something else?
Looking at my BTC Guild account, I see no evidence of any blocks found by my computer.

This means your pool server has accepted one block, generated your CPU, third thread, of difficulty 288 (with a minimum of two).

If this was generated by my CPU, that is odd because BTC Guild does not show any contributions from my computer.

That's odd, is your "worker name" correct in bfgminer?  In BTCGuild, in the "Your Recent PPLNS Shift Statistics" window of the Dashboard page, are any of the numbers in the "Shares" column non-zero?

Does the user need to care about the difficulty and its minimum?


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Is it profitable to use Amazon EC2 to mine litecoins?
I saw that mining BTC with CPU is not profitable anymore, and that you'd lose money mining bitcoin. Is the same thing true of litecoin?

While the other question was technically about mining BTC and as such is not technically a duplicate, LTC mining on an EC2 node was discussed in an answer to this question

Yes it can be worth it, but generally what happens is if it ever is worth it then a huge number of people start doing it until the prices of EC2 are driven up and it is no longer profitable. Here is a good blog post about the subject:
http://da-data.blogspot.com/2013/12/briefly-profitable-alt-coin-mining-on.html

Only if you use the micro instance with a free account for the first year.


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Is it possible to cancel an unconfirmed transaction?
If you submit a transaction to the network but it hasn't yet be confirmed by a block, is it possible to cancel this transaction?

Is it not confirming because it is an invalid transaction (double-spend) or just low priority / spammy and thus could take a day or so?

Bitcoin-Qt doesn't support anything like that.
Theoretically:
A transaction is canceled by publishing a second transaction which double-spends some of the coins used in the first transaction (this can be a send-to-self). If the second transaction is included in a block before the first one, the first one becomes invalid and can be considered fully cancelled after the second transaction receives 6 confirmations. It's normally not easy to do this. Network nodes won't accept transactions which double-spend coins used in a transaction they already know about. However, nodes gradually forget about transactions if they don't get into blocks, so a transaction could be cancelled if it doesn't make it into a block after several days and both the sender and recipient stop rebroadcasting it.
Bitcoin used to have a feature called transaction replacement. A transaction could be marked as non-final, which prevented this transaction from getting into a block, but allowed the transaction to be cancelled at any time. Satoshi disabled this a while ago, though. Transactions can still be marked as non-final, but they can't be replaced.

What's the point of marking a transaction non-final, then? A lot of what's at https://en.bitcoin.it/wiki/Contracts seems to require replacing transactions which were marked non-final.

@DanielH It should be possible to communicate non-final transactions privately and only broadcast the final version of the transaction. Currently, though, one of the parties can publicly broadcast a non-final transaction, and this non-final transaction can't be replaced by a later version of the transaction. This causes problems for some contracts. Nodes should probably just reject non-final transactions if they're not going to allow replacements.

At present, for practical purposes, it's impossible to do this. In theory, miners should be happy to replace a transaction with a conflicting transaction with a higher fee. But to my knowledge, nobody implements this. The consensus seems to be that it's more valuable to the community to have unconfirmed transactions be more reliable.

If the second transaction has a higher fee, the chances of it getting accepted are high.

@Jus12 {{citation needed}}

@Lohoris If you realize that a fee is a bid for a miner to accept transactions, and as the reward keeps decreasing, it is more advantageous for miners to drop a lower fee transaction from a double spend.

@Jus12 it would be more advantageous, but AFAIK no miner actually does that, hence your sentence is wrong. Until you prove otherwise.

Do I properly understand that in case I've broadcasted the transaction of, for example, 1BTC with super low fee when the mempool is heavily loaded and my wallet, for example, has 10BTC - to cancel the first one, that is still unconfirmed, I need to send 10BTC to myself with normally high fee, so that 1BTC transaction will be out of place?

From the help of the console :

abandontransaction "txid"

That will tag the transaction as abandonned
 "abandoned": true

After that, you can reselect the input(s) to send it with higher fees
Tested in bitcoin core 0.12.1

does this work for non wallet id transactions in any way ?

@ShabahatM.Ayubi only with in-wallet transactions https://bitcoin.org/en/developer-reference#abandontransaction The abandontransaction RPC marks an in-wallet transaction and all its in-wallet descendants as abandoned. This allows their inputs to be respent. Abandons the transaction on your node.


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How can the blockchain survive without an army or other kind of law enforcement?
I'm sold on most of the Bitcoin aspects. I believe that the blockchain has incredible potential value and how the fact that it's decentralized removes a lot of the corruption and cronyism that are rampant in today's centralized institutions.
However one thing I don't get is how does the contract, or property or other value that you have stored in the blockchain is enforced? Surely some people won't care that the proof of property of your land is in the blockchain and just claim it with guns. What do you do then? How is this sorted? States have judicial and military power. What does the blockchain have?

The blockchain itself does not have any power. It is just public set of records, like a phonebook.
Depending on the contract between trading parties, you arbitrage the contract disputes within the legal means you have available.
However, blockchain can act as a proof of agreement and everything signed there is very hard to forge: the other party cannot claim they did not sign the agreement if the private key used in signing can be proven to belong to the party.

But since the private key of the other party is private if it is not supplied there can be no proof that they signed it, just that someone signed it. There is no "nonrepudiation" available.

Zaph, are you sure? I thought the point of public key cryptography was that you sign with the private key and verify with the public key. If I'm correct, then one would only need the public key to verify that it was signed.

The blockchain survives by having nodes which continue to keep it up to date which implies having a network which allows those to communicate.
As far as the question of someone ignoring the blockchain, since all transactions take place in the blockchain there is no such thing as a bitcoin transaction apart from the blockchain.
To put it in other words proof of ownwership of bitcoins requires two things.
1) Here, look, I have a private key.
2) Here, look, the blockchain says that this private key has some quantity of bitcoins associated with it.
In this context since the bitcoin nodes keep the blockchain correct, the only other way of obtaining bitcoins is via the obtaining of a private key by force, theft, whatever.


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How is the probability of winning a block calculated from the difficulty?
I have problem finding this. The Bitcoin wiki mentions the probability here, but only with a link to the current value on BlockExplorer.
The wiki page on difficulty doesn't mention the formula for the probability either.

What probability are you after? The probability of a hash solving a block (as per Peter's explanation), or a share solving a block? Or the number of blocks you might solve or shares you might submit in a given time period?

The probability of a hash solving a block. I don't know how the share system works, isn't that implemented differently for each different pool specification?

Yes, variable difficulty shares means that strictly speaking "shares per block" is meaningless. In this context though most would take "shares per block" to mean "Difficulty 1 shares per block", which have a probability of exactly 1/Difficulty.

If the current difficulty is D, then the target hash (the value below which block hashes must go) is:

0x00000000FFFF0000000000000000000000000000000000000000000000000000 / D

(by definition of difficulty, which is a fraction of the maximum target), or otherwise put, the number of valid hashes is:

65535 * 2208 / D

Which means that the ratio of all hashes over valid hashes would be:

2256 / (65535 * 2208 / D) =
  D * 248 / 65535 =
  D * 4295032833

Which, at the current (January 2017) difficulty of D =  392963262344.3704 means that one hash in

392963262344.3704 * 4295032833 = 1687790113931869416948

results in a valid block, or each attempt has a chance of

1 / 1687790113931869416948 = 0.000000000000000000059 %

I think the third equation is the formula for all possible hashes, not "the fraction of valid hashes to all possible hashes", isn't it? Shouldn't there be a "1/" in front?


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What happens when a coin is split?
The original Bitcoin paper states:

We define an electronic coin as a chain of digital signatures.

What happens when a coin is subdivided and transferred to multiple owners? Does each coin fragment form its own chain of digital signatures, or are all the fragments still part of this one original chain of digital signatures?

Each fragment starts it's own chain.
Edit: I randomly selected a transaction for you to see.  Try this link: http://blockchain.info/tree/7514743 and click on the yellow circles.
Edit2:: Actually, this one is more interesting: http://blockchain.info/tree/50429084  In the former, the payments mostly returned in part to the original address.  That's odd.  The usual way of doing things is sending to one address and returning to yourself at yet another address.

Do you have a reference?

Just added a random transaction for you to inspect.


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Coinbase maturity of 100 transactions
The protocol rules state that

For each input, if the referenced output transaction is coinbase (i.e.
  only 1 input, with hash=0, n=-1), it must have at least
  COINBASE_MATURITY (100) confirmations; else reject this transaction

Why should coinbase transactions with less than 100 confirmations be unspendable? What is the point of the rule?

The answer to this question is the second answer in the above linked question.

The reason for this is that if a fork were to occur, some blocks will be orphaned and not have any coins which can be rebroadcast. If a block containing a transaction you send me gets orphaned, I can still get my coins, but if the block you are sending me coins from gets orphaned, I can not rebroadcast since the coinbase no longer exists on the valid chain.

But the chances of such a massive fork is basically zero.

You say that now ;)


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How do Bitcoin nodes know where to send new transactions and blocks to?
I am researching Bitcoin; what I can't find much information on though is how the P2P network itself operates. For example, BitTorrent uses a DHT protocol that allows for node discovery and calculating distances between nodes etc.
So if a Bitcoin client wants to do a transaction, how does it know which IP address to connect to in order to announce it?
And how does the node that the transaction gets sent to know which other nodes it needs to connect to, and so on?

Not really a duplicate: the question is mostly about how data moves through the network, not actually about how peers are found (I think).

The question is based on the false premise that nodes decide which other nodes to connect to based on what they need to do. That's just not how Bitcoin works.

Bitcoin is a so-called gossip network. They announce any new object to all of their peers (just the hash of the data). If the peer doesn't know the object yet, it asks for the full object. So it's certainly not a DHT or any smart organisation of data: every (full) node (eventually) learns about every block and transaction. They have to, there is no other way of validating history otherwise.
As for how the client discovers peers, see How do Bitcoin clients find each other?

If you want to know how peers are found: see the link to the potential duplicate (it's independent from what you want to do). If you want to know where blocks and transactions get sent, it'd easy: everywhere.


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Can I use an old Pentium 4 desktop for mining if I upgrade it with a good GPU?
I know that the most important thing for mining is a GPU. I read some stuff about it but I never read a specific answer to this simple question.
I have some old desktop computer. Pentium 4 (~1GHz) processor and (maybe 256-)512 MBs or RAM.
Can I use this computer as a base for a simple mining machine if I can just put in a decent GPU??
I'm just strolling the internet for second-hand GPUs and asking friends, but I cannot afford to invest too much in it, so I'd like to be able to use that desktop for my setup.

PCI-e on the mobo?

With a decent enough GPU (or GPUs), your machine will be a fine miner. The only spec that ACTUALLY matters for mining is the GPU. RAM, CPU, etc don't have much of an impact.

It is possible, but you really should first pause for a moment and consider a few things before proceeding further:

What graphics card will you buy - Go to this wiki page, look which graphics cards are good and then do a search for what you can find in stores. If you're looking for the most efficient mining cards, you might not find them, so you should take that into account.
Check whether your motherboard can support said graphics card (shoudln't be an issue in most cases), whether it will fit in your computer case (can be an issue if it is very small or crammed), and whether your power supply can handle it (which probably will be an issue with higher-end cards).
Check whether mining is really the thing you want to be doing - the profit margins might not be too high at the moment. You can for example use my mining calculator - put in how much your graphics card and power supply will cost you, how much power the whole computer will consume, how fast you'll be hashing, and how much does electricity cost you. It might turn out that you'll be mining at a loss. Even if you are not in red, lower the price of Bitcoins a bit and see whether you are still profitable. Difficulty appears to be rising slowly and the price of Bitcoins can always go down, so you have to be mindful that what you can get at the moment might not be the same as what you can get in the future.

If everything appears to be in order for you, you can try going for it, otherwise you might want to consider just buying some Bitcoins at an exchange and hoping the price will rise. So all in all, it is possible to use your old hardware with a new graphics card to profitably mine Bitcoins, but you have to consider a few factors before making the decision.
As for a pool that is good for a small miner, basically any of them work. Compare them and pick whichever works best for you.

How can I check what graphic cards my motherboard supports?
Points 1 and 3 are ok. I wanna start mining for sure, but just on small scale. It wouldn't that kind a risico if I can use that desktop machine i have because I have free electricity in my student home, so other than the GPU I won't have any other costs :)

@stevenroose Check what slot does your motherboard have for graphics card - whether it is AGP, PCI-e or the like. Just look up your motherboard's model number online and you should find the information.

It's likely that your motherboard supports only AGP video cards. It's unlikely that you will be able to find a video card with AGP that will provide a decent price/performance ratio, taking into account the cost of the card (minimal for something so old) and electric consumption.
The Radeon HD 4670 entry on the MHC lists ~40 Mhash/s. That's less than 1 BTC. At $5/BTC exchange rate, you're making ~$4/mo. If your power is free or ultra cheap, it might be worth it, but you're still making less than 1 BTC/month.
Unless the exchange rate shoots up, it's probably not worth it.

How can I check what graphic cards my motherboard supports?

Does it look like an AGP slot or a PCI Express slot (the two longer ones depicted)? You may also be able to use a regular PCI video card, but that's unlikely be be worthwhile for similar reasons that AGP is not worthwhile.

I think it's a AGP slot, it's not mentioned anywhere on the hardware. But it looks brown (like I saw AGP being in pictures). But I also have several (4) white slots, of which some were used by some ethernet-like plug and some for audio I guess.
Are these PCI? I have no idea, never been that hard into hardware :)
Can I use those maybe?

I must say this is amusing to read in 2017 :)

As ThePiachu says, the PSU needs to be suitable.
Some graphics cards require 2 (or even 4, I think) molex cables from your power supply to provide additional power. The wattage from your power supply needs to be adequate to power all the components connected to it, and cheap PSU's often don't even provide their stated wattage (or clean enough output to power for a gfx card). Further, approaching the stated maximum wattage for a given PSU pushes its fan into overdrive and can be extremely noisy. You may need to buy additional cooling fans the help keep the graphics card cool, which draw addional power and need additional cables from the PSU.
I find this website particularly helpful in picking an appropriate PSU for my PCs:
http://www.silentpcreview.com/section10.html
Check out this thread to see some typical (and atypical!) mining rigs:
https://bitcointalk.org/index.php?topic=7216.0


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What is the minimum investment for Bitcoin?
I'm interested in how much money do I have to invest if I want to buy Bitcoins? Is there any minimum?

he factors that matter in order to give you the best answer include: Where are you located (country)?, how much are you looking to buy?, what payment methods do you have available?, how soon do you need access to the proceeds, is privacy important?

I disagree with the close vote. There's a perception that Bitcoin is a merely a security, so this question could serve as a way of dispelling that myth by explaining that there is no minimum investment like there can be for securities.

On the whole, there is no minimum investment for Bitcoin, as it is not a security such as an ETF or mutual fund purchased through a brokerage or management firm.
What minimum purchases exist on Bitcoin exchanges are merely requirements set by each individual exchange to reflect the minimum purchase/sale that they feel is necessary to cover their overhead for each transaction.
Purchasing from an individual trader, you'll find that there is generally no such minimum, aside from whatever minimum they set to make it worth the time and travel expense for a rendezvous.

Most exchanges have no minimum deposit however there are per-transaction fees which make smaller deposits uneconomical.
The cost to deposit funds varies based on each exchange and each country.


text:
Is it more efficient to use multiple computers when I have multiple GPUs?
I have 4 video cards: 2x 7970 & 2x 6970.
This is a question of efficiency regarding MH/s. Simply, I would like to know which is better:

~1900 MH/s on one machine
~1200 MH/s and ~700 MH/s on respective machines
It does not matter

Could the answer please include efficiency for both solo mining and pool mining?

More efficient in terms of Hash/Second, Hash/$ or Hash/Watt?

@NickODell I reworded the question.

This is a question of efficiency regarding MH/s. Simply, I would like to know which is better

It doesn't matter. Every hash has an equal probability of finding a block. However, that being said, there's some hidden teeth:

Putting graphics cards together will make them harder to cool.
Putting them in multiple computers will use more electricity - all computers use some electricity, even at idle.

Could the answer please include efficiency for both solo mining and pool mining?

My advice applies for both.

If I had a solution for the cooling problem, would you consider having 3 cards in one box to be the best solution?

@user4543 Yeah.