question: why does putting "www" before the address matter for some sites but not others?
comment: Originally, the world wide web was just a small part of the internet. The internet included the world wide web, but it also included FTP (file transfer protocol), e-mail (okay, we still have that), Usenet (bulletin boards), and more. So, if you buy a domain, say URL_0 , then you would put your webpage on www. URL_0 , and you would put your files on ftp. URL_0 , and your email address might be at mail. URL_0 . But as time progressed, the world wide web eclipsed much of those, so we figured it would be easier to type in URL_1 as opposed to www. URL_1 , and here we are!
passages: When a user submits an incomplete domain name to a web browser in its address bar input field, some web browsers automatically try adding the prefix "www" to the beginning of it and possibly ".com", ".org" and ".net" at the end, depending on what might be missing. For example, entering " may be transformed to "http://www.microsoft.com/" and 'openoffice' to "http://www.openoffice.org". This feature started appearing in early versions of Firefox, when it still had the working title 'Firebird' in early 2003, from an earlier practice in browsers such as Lynx. It is reported that Microsoft was granted a US patent for the same idea in 2008, but only for mobile devices.
   Many hostnames used for the World Wide Web begin with "www" because of the long-standing practice of naming Internet hosts according to the services they provide. The hostname of a web server is often "www", in the same way that it may be "ftp" for an FTP server, and "news" or "nntp" for a Usenet news server. These host names appear as Domain Name System (DNS) or subdomain names, as in "www.example.com". The use of "www" is not required by any technical or policy standard and many web sites do not use it; the first web server was "nxoc01.cern.ch". According to Paolo Palazzi, who worked at CERN along with Tim Berners-Lee, the popular use of "www" as subdomain was accidental; the World Wide Web project page was intended to be published at www.cern.ch while info.cern.ch was intended to be the CERN home page, however the DNS records were never switched, and the practice of prepending "www" to an institution's website domain name was subsequently copied. Many established websites still use the prefix, or they employ other subdomain names such as "www2", "secure" or "en" for special purposes. Many such web servers are set up so that both the main domain name (e.g., example.com) and the "www" subdomain (e.g., www.example.com) refer to the same site; others require one form or the other, or they may map to different web sites. The use of a subdomain name is useful for load balancing incoming web traffic by creating a CNAME record that points to a cluster of web servers. Since, currently, only a subdomain can be used in a CNAME, the same result cannot be achieved by using the bare domain root.
   As the mobile Web grew in popularity, services like Gmail.com, Outlook.com, Myspace.com, Facebook.com and Twitter.com are most often mentioned without adding "www." (or, indeed, ".com") to the domain.
  
  Section::::Function.:Scheme specifiers.
   An abbreviation "W" ( "double-u cubed") is inspired from mathematical notation for exponentiation (W raised to the 3rd power). Many of the original papers describing the World Wide Web abbreviated it this way, and the World Wide Web Consortium (W3C) was named according to this early usage. The original W3C logo had a superscript "3" and the consortium's domain name is still codice_1.
  
  Section::::Other languages.
  
  In Afrikaans, Dutch, German, Polish and other languages, this problem doesn't occur because the letter W is already uttered as a single syllable.
   Some organisations situated in Switzerland use TLDs to specifically refer to their canton (such as the Belgian TLD .be for the Canton of Berne).
  
  In Turkish, "biz" means "we", and can be used for emphasis at the end of "we are" sentences.
   A website may have multiple home pages, although most have one. Wikipedia, for example, has a home page at wikipedia.org, as well as language-specific home pages, such as en.wikipedia.org and de.wikipedia.org.
  
  Section::::Website home page.:Website structure.
  
  The majority of websites have a home page with underlying content pages, although some websites contain only a single page.
  
  The uniform resource locator (URL) of a home page is most often the base-level domain name, such as https://wikipedia.org. Historically it may also be found at http://domain.tld/index.html or http://domain.tld/default.html, where "tld" refers to the top-level domain used by the website.
   In the early days of the World Wide Web in the first half of the 1990s, an important part of web pages belonged to students or teachers with a UNIX account in their university. System administrators of such systems installed an HTTP server pointing its root directory to the directory containing the users accounts. On UNIX, the base directory of an account is called "home", and the codice_1 environment variable contains its path (for example codice_2). The URL of the home page usually has the format codice_3. Thus the term home page appeared and then spread to its current usage.
   If a home page has not been created for a web site, many web servers will default to display a list of files located in the site's directory, if the security settings of the directory permit. This list will include hyperlinks to the files, allowing for simple file sharing without maintaining a separate HTML file.
  
  Section::::Browser home page.
   While a hostname may not contain other characters, such as the underscore character ("_"), other DNS names may contain the underscore. Systems such as DomainKeys and service records use the underscore as a means to assure that their special character is not confused with hostnames. For example, "_http._sctp.www.example.com" specifies a service pointer for an SCTP-capable webserver host (www) in the domain "example.com". Notwithstanding the standard, Chrome, Firefox, Internet Explorer, Edge and Safari allow underscores in hostnames, although cookies in IE do not work correctly if any part of the hostname contains an underscore character. 
   In English, "www" is usually read as "double-u double-u double-u". Some users pronounce it "dub-dub-dub", particularly in New Zealand. Stephen Fry, in his "Podgrams" series of podcasts, pronounces it "wuh wuh wuh". The English writer Douglas Adams once quipped in "The Independent on Sunday" (1999): "The World Wide Web is the only thing I know of whose shortened form takes three times longer to say than what it's short for". In Mandarin Chinese, "World Wide Web" is commonly translated via a phono-semantic matching to "wàn wéi wǎng" (), which satisfies "www" and literally means "myriad dimensional net", a translation that reflects the design concept and proliferation of the World Wide Web. Tim Berners-Lee's web-space states that "World Wide Web" is officially spelled as three separate words, each capitalised, with no intervening hyphens. Use of the www prefix has been declining, especially when Web 2.0 web applications sought to brand their domain names and make them easily pronounceable.
   Some browsers and software applications do not properly recognize new gTLDs as top-level domains. For example, some browsers do not recognize many new gTLDs and instead treat them as a search query. Prefixing the domain with "http://", or including a trailing slash, will usually force the browser to perform a DNS lookup rather than a search.
  
  Section::::Expansion of gTLDs.:Criticism.
   The domain name is a component of a uniform resource locator (URL) used to access web sites, for example:
  
  BULLET::::- URL: http://www.example.net/index.html
  
  BULLET::::- Top-level domain: net
  
  BULLET::::- Second-level domain: example
  
  BULLET::::- Host name: www
  
  A domain name may point to multiple IP addresses to provide server redundancy for the services offered, a feature that is used to manage the traffic of large, popular web sites.
   The contents of a web page are arbitrary and controlled by the entity owning the domain named displayed in the address bar. If HTTPS is used, then encryption is used to secure against attackers with access to the network from changing the page contents en route. When presented with a password field on a web page, a user is supposed to look at the address bar to determine whether the domain name in the address bar is the correct place to send the password. For example, for Google's single sign-on system (used on e.g. youtube.com), the user should always check that the address bar says "https://accounts.google.com" before inputting their password.
   The Resolution declared that "having a Top Level Domain name for our city will put us on par with other global cities that have Top Level Domain names: Singapore (.SG), Hong Kong (.HK), the Vatican (.VA), and Los Angeles (.LA) - note: Los Angeles uses the domain name originally issued to Laos. ... Having a .NYC TLD will make our community more governable, provide opportunities for small businesses, raise city revenue, and make navigating the Internet easier for our residents, prospective tourists, and businesses."
   BULLET::::- A hostname is a domain name that has at least one associated IP address. For example, the domain names "www.example.com" and "example.com" are also hostnames, whereas the "com" domain is not. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames.
  
  BULLET::::- Hostnames impose restrictions on the characters allowed in the corresponding domain name. A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname.
  
  Section::::Domain name space.:Top-level domains.
   With the 2005 announcement that registration of the remaining single-letter names might become available, some companies have attempted to establish a right to the names by claiming trademark rights over single letters used in such a context. "U" magazine, a college oriented publication, went so far as to re-brand its website as "U.com" and apply for a trademark registration of the same phrase, before sending a letter to ICANN attempting to gain priority for the domain if it should ever become available in the future.
  
  Section::::External links.
  
  BULLET::::- ICANN - Reserved domain names
   Pronunciation of &quot;www&quot;
  
  WWW (or www) is an initialism for World Wide Web. In English, WWW is the longest possible three-letter abbreviation when spoken, requiring six to nine syllables, depending on how it is pronounced, whereas the twelve letters in "World Wide Web" are pronounced with three syllables. The English writer Douglas Adams once quipped:
  
  Tim Berners-Lee rejected suggestions to change the World Wide Web name over pronunciation issues, arguing that this peculiar feature of the name would make it memorable. As his invention gradually gained ubiquity, it came to be called simply "the Web".
  
  Section::::English pronunciation.
   Second-level (or lower-level, depending on the established parent hierarchy) domain names are often created based on the name of a company (e.g., "bbc".co.uk), product or service (e.g. "hotmail".com). Below these levels, the next domain name component has been used to designate a particular host server. Therefore, "ftp.example.com" might be an FTP server, "www.example.com" would be a World Wide Web server, and "mail.example.com" could be an email server, each intended to perform only the implied function. Modern technology allows multiple physical servers with either different (cf. load balancing) or even identical addresses (cf. anycast) to serve a single hostname or domain name, or multiple domain names to be served by a single computer. The latter is very popular in Web hosting service centers, where service providers host the websites of many organizations on just a few servers.
   In some languages, such as Danish, Estonian, Finnish, Norwegian, and Swedish it is common practice to say "ve"("v") instead of "dobbelt-ve" in abbreviations, so "www" becomes "ve, ve, ve". This is also used by Romanian, Serbian, etc. In Danish, it is also usual to say "tre gange dobbelt-ve" ("three times double u").
  
  In many languages which give the letter "W" a name that translates to "double V", each "w" is substituted by a "v", so "www" is shortened to "vvv" instead. Another practice is to use a numeric shortcut that translates "w-w-w" as "triple W".
   Most of the world follows the Internet standard and writes email addresses starting with the name of the computer and ending up with the name of the country. In the U.K. the Joint Academic Networking Team (JANET) had decided to do it the other way round before the Internet domain standard was established. Most gateway sites have ad-hockery in their mailers to handle this, but can still be confused. In particular, the address me@uk.ac.bris.pys.as could be interpreted in JANET's big-endian way as one in the U.K. (domain uk) or in the standard little-endian way as one in the domain as (American Samoa) on the opposite side of the world.
   BULLET::::- Common Domain Cookie Reading Service
  
  As a hypothetical example of a "Common Domain", let's suppose Example UK (example.co.uk) and Example Deutschland (example.de) belong to the virtual organization Example Global Alliance (example.com). In this example, the domain example.com is the common domain. Both Example UK and Example Deutschland have a presence in this domain (uk.example.com and de.example.com, resp.).
   Subdomains of "name" may be registered at the second-level ("john".name) and the third-level ("john".doe.name). It is also possible to register an e-mail address of the form "john@doe.name". Such a registration may require another address as destination. The second-level domain of third-level subdomains is shared, and may not be registered by individuals.
  
  When the TLD "name" was first launched, only third-level registrations and forwarded e-mail addresses were available. Second-level registrations became available in January 2004. The original intended structure of domain names was "first.last.name", so that individuals could get a domain corresponding to their name.
   Many people choose a domain name like "FirstnameLastname.com" to host their personal website on (e.g., patxhosa.com), whereas outside the English-speaking world, the home country's top level domain (TLD) is commonly used. People with common names may choose to add their middle name or initial in the URL if the primary choice of domain name is already in use. For example, a woman named "Jane Doe" will probably find that "janedoe.com" is already taken, so she may have to use a variant of her name, such as adding in a number ("janedoe1.com"), a birth year ("janedoe1980.com") or a middle initial ("janeqdoe.com"). The .name TLD is specifically intended to be used for personal web pages, but has not proven to be popular. Personal websites may instead use other generic TLDs like .me, .co, .net and .info, but also .com, .biz and .org, even though individuals rarely think of themselves as companies or (non-profit) organizations. Some people opt to find a TLD that forms a word when combined with the domain name; this is known as domain hacking.
   While "web site" was the original spelling (sometimes capitalized "Web site", since "Web" is a proper noun when referring to the World Wide Web), this variant has become rarely used, and "website" has become the standard spelling. All major style guides, such as "The Chicago Manual of Style" and the "AP Stylebook", have reflected this change.
  
  Section::::Types.
   BULLET::::- Removing or adding “www” as the first domain label. Some websites operate identically in two Internet domains: one whose least significant label is “www” and another whose name is the result of omitting the least significant label from the name of the first, the latter being known as a naked domain. For example, codice_40 and codice_2 may access the same website. Many websites redirect the user from the www to the non-www address or vice versa. A normalizer may determine if one of these URLs redirects to the other and normalize all URLs appropriately. Example:
  