question: Why do graphics cards use GDDR6 RAM but RAM in our phones, PCs, etc are DDR4?
comment: After GDDR4/DDR3, GDDR spit off to be a different style of RAM with different goals. Graphics memory requires obscenely high throughput, but some latency is acceptable as they're only looking to draw a frame every few milliseconds or so and all graphical tasks can go in parallel so the GPU tends to pull large chunks of data which makes the higher latency hurt less. Your CPU needs low latency memory because it is often waiting for something to come out of memory so it can keep calculating. Its often looking for a single chunk of data which is where latency hurts you the most. You don't want to use GDDR6 as main memory as it will hurt the CPU's performance, and you don't want to use DDR4 as GPU RAM as it'll limit the GPU's performance. This is why we split them apart after GDDR4 which was DDR3 based, so each computing device could have the best memory for its workload.
passages: BULLET::::2. Be "registered" ("buffered"), which improves signal integrity (and hence potentially clock rates and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, whereas non-registered (a.k.a. "unbuffered") RAM "may be" identified by an additional U in the designation. PC2-4200R is a registered PC2-4200 module, PC2-4200R ECC is the same module but with additional ECC.
   The memory capacity of most modern video cards ranges from 1 GB to 12 GB. Since video memory needs to be accessed by the GPU and the display circuitry, it often uses special high-speed or multi-port memory, such as VRAM, WRAM, SGRAM, etc. Around 2003, the video memory was typically based on DDR technology. During and after that year, manufacturers moved towards DDR2, GDDR3, GDDR4, GDDR5 and GDDR5X. The effective memory clock rate in modern cards is generally between 1 GHz to 10 GHz.
   GDDR3 and GDDR5 is now commonly used in modern graphics cards and some tablet PCs. However, further confusion has been added to the mix with the appearance of budget and mid-range graphics cards which claim to use "GDDR2". These cards actually use standard DDR2 chips designed for use as main system memory although operating with higher latencies to achieve higher clockrates. These chips cannot achieve the clock rates of GDDR3 but are inexpensive and fast enough to be used as memory on mid-range cards.
  
  Section::::See also.
  
  BULLET::::- DDR SDRAM
  
  BULLET::::- CAS latency (definition of "CAS 5-5-5-15", for example)
   The GDDR6 memory is produced by Samsung Electronics for the Quadro RTX series. The RTX 20 series initially launched with Micron memory chips, before switching to Samsung chips by November 2018.
  
  Section::::Details.:Rasterization.
  
  Nvidia reported rasterization (CUDA) performance gains for existing titles of approximately 30–50% over the previous generation.
  
  Section::::Details.:Ray-tracing.
   BULLET::::- DDR4 memory support updated for 2666 MHz (for i5, i7 and i9 parts) and 2400 MHz (for i3 parts); DDR3 memory is no longer supported on LGA1151 parts, unless using with H310C chipset
  
  BULLET::::- 300 series chipset on the second revision of socket LGA 1151
  
  Section::::Kaby Lake Refresh vs. Coffee Lake.
   The following year (2015) was a crucial year for the standardization of plug-and-play DDR4-based NVDIMM cards. These persistent memory devices reside on the processor's memory subsystem, which requires broader platform support, but is a better fit, because it was designed for memory-like latencies and cache-line granular access. 2015 also saw several key announcements of new storage-class memory (SCM) based devices, such as Intel & Micron 3D XPoint, HPE & SanDisk memristors, Samsung & "Netlist" NVDIMM-P and Sony & "Viking Technology".
  
  Section::::Description.
   Most significant, the supply voltage is reduced from 2.5 to 1.8 V. Additional savings come from temperature-compensated refresh (DRAM requires refresh less often at low temperatures), partial array self refresh, and a "deep power down" mode which sacrifices all memory contents. Additionally, chips are smaller, using less board space than their non-mobile equivalents. Samsung and Micron are two of the main providers of this technology, which is used in tablet and phone devices such as the iPhone 3GS, original iPad, Samsung Galaxy Tab 7.0 and Motorola Droid X.
  
  Section::::Generations.:LP-DDR2.
   BULLET::::- Number of DRAM devices: The number of chips is a multiple of 8 for non-ECC modules and a multiple of 9 for ECC modules. Chips can occupy one side ("single sided") or both sides ("dual sided") of the module. The maximal number of chips per DDR module is 36 (9×4) for ECC and 32 (8x4) for non-ECC.
  
  BULLET::::- ECC vs non-ECC: Modules that have error-correcting code are labeled as ECC. Modules without error correcting code are labeled non-ECC.
   BULLET::::- Mali-400 MP4 GPU, up to 600 MHz (typically 533 MHz) supporting OpenGL ES 1.1/2.0, Open G 1.1
  
  BULLET::::- High performance dedicated 2D processor
  
  BULLET::::- DDR3, DDR3L, LPDDR2 support
  
  BULLET::::- Dual-panel display up to 2048x1536 resolution
   BULLET::::- DDR SDRAM memory interface
  
  BULLET::::- Rendition V4400 graphics core with 4 MB embedded DRAM. Can use system RAM as well.
  
  BULLET::::- PCI interface, USB interface, Ultra ATA 66, AC'98 audio controller, IEEE 1394 interface
  
  Section::::Games with Rendition support.
   Despite being designed by ATI, the first card to use the technology was nVidia's GeForce FX 5700 Ultra in early 2004, where it replaced the GDDR2 chips used up to that time. The next card to use GDDR3 was nVidia's GeForce 6800 Ultra, where it was key in maintaining reasonable power requirements compared to the card's predecessor, the GeForce 5950 Ultra. ATI began using the memory on its Radeon X800 cards. GDDR3 was Sony's choice for the PlayStation 3 gaming console's graphics memory, although its nVidia based GPU is also capable of accessing the main system memory, which consists of XDR DRAM designed by Rambus Incorporated (Similar technology is marketed by nVidia as TurboCache in PC platform GPUs). Microsoft's Xbox 360 has 512 MB of GDDR3 memory. Nintendo's Wii also contains 64 MB of GDDR3 memory.
   BULLET::::3. Non-registered (a.k.a. "unbuffered") RAM "may be" identified by an additional U in the designation.
  
  BULLET::::4. Fully buffered modules, which are designated by F or FB and do not have the same notch position as other classes. Fully buffered modules cannot be used with motherboards that are made for registered modules, and the different notch position physically prevents their insertion.
   Section::::Third-party chips.:VRC7.
  
  BULLET::::- Manufacturer: Konami, Yamaha
  
  BULLET::::- Games used in: "Lagrange Point", ""
  
  The VRC7 is a very advanced MMC chip from Konami, not only supporting bank switching and IRQ counting equivalent to the VRC6 but also containing a YM2413 derivative providing 6 channels of FM Synthesis audio. This advanced audio is used only in the Famicom game "Lagrange Point"; while the Japanese version of "Tiny Toon Adventures 2" also used the VRC7, it does not make use of the extended audio.
  
  Section::::Third-party chips.:Namco 163.
  
  BULLET::::- Manufacturer: Namco
   BULLET::::- Max. 1.72 GB RAM; virtual memory is not supported.
  
  BULLET::::- Only Radeon cards have support; Nvidia cards are not supported.
  
  Section::::Supported hardware.:Amiga.
  
  BULLET::::- Amiga 1200 with Blizzard PPC accelerator card
  
  BULLET::::- Amiga 3000 with CyberStorm PPC accelerator card
  
  BULLET::::- Amiga 4000 with CyberStorm PPC accelerator card
  
  Section::::Supported hardware.:Apple.
  
  BULLET::::- Mac mini G4
  
  BULLET::::- eMac
  
  BULLET::::- Power Mac G4
  
  BULLET::::- PowerBook G4 (except for 12" aluminum models)
  
  BULLET::::- iBook G4
  
  BULLET::::- Power Mac G5
  
  BULLET::::- Power Mac G4 Cube
  
  Section::::Supported hardware.:Genesi/bPlan GmbH.
  
  BULLET::::- EFIKA 5200B
  
  BULLET::::- Pegasos I G3
  
  BULLET::::- Pegasos II G3/G4
  
  Section::::Supported hardware.:ACube.
  
  BULLET::::- Sam460 series mainboards
   BULLET::::- Clock Speeds: This is the clock speed that the graphics core and video RAM run at; they do not need to be the same. The faster the clock speed, the more the graphics core and/or video RAM can accomplish in a second. All modern video cards use DDR SDRAM, which, for all performance issues, is twice as fast as its actual clock speed indicates. All clock speeds mentioned here for DDR RAM are their effective "DDR speeds," and their actual clock speeds are half that.
   RDRAM was a particularly expensive alternative to DDR SDRAM, and most manufacturers dropped its support from their chipsets. DDR1 memory's prices substantially increased since Q2 2008, while DDR2 prices declined. In January 2009, 1 GB DDR1 was 2–3 times more expensive than 1 GB DDR2. High-density DDR RAM suit about 10% of PC motherboards on the market, while low-density suit almost all motherboards on the PC Desktop market.
  
  Section::::Generations.:Mobile DDR.
   In February 2005, Samsung demonstrated the first DDR3 memory prototype, with a capacity of 512Mb and a bandwidth of 1.066Gbps. Products in the form of motherboards appeared on the market in June 2007 based on Intel's P35 "Bearlake" chipset with DIMMs at bandwidths up to DDR3-1600 (PC3-12800). The Intel Core i7, released in November 2008, connects directly to memory rather than via a chipset. The Core i7 supports only DDR3. AMD's first socket AM3 Phenom II X4 processors, released in February 2009, were their first to support DDR3.
  
  Section::::Overview.:Dual-inline memory modules.
   Products using LPDDR3 include the 2013 MacBook Air, iPhone 5S, iPhone 6, Nexus 10, Samsung Galaxy S4 (GT-I9500) and Microsoft Surface Pro 3. LPDDR3 went mainstream in 2013, running at 800 MHz DDR (1600 MT/s), offering bandwidth comparable to PC3-12800 notebook memory in 2011 (12.8 GB/s of bandwidth). To achieve this bandwidth, the controller must implement dual-channel memory. For example, this is the case for the Exynos 5 Dual and the 5 Octa.
   BULLET::::- Are not backwards compatible—DDR3 modules do not fit into DDR2 sockets; forcing them can damage the DIMM and/or the motherboard
  
  Section::::Feature summary.:Technological advantages over DDR2.
  
  BULLET::::- Higher bandwidth performance, up to 2133 MT/s standardized
  
  BULLET::::- Slightly improved latencies, as measured in nanoseconds
  
  BULLET::::- Higher performance at low power (longer battery life in laptops)
  
  BULLET::::- Enhanced low-power features
  
  Section::::Development and market penetration.
   Section::::Modules.
  
  Section::::Modules.:JEDEC standard DDR4 module.
  
  BULLET::::- CAS latency (CL): Clock cycles between sending a column address to the memory and the beginning of the data in response
  
  BULLET::::- tRCD: Clock cycles between row activate and reads/writes
  
  BULLET::::- tRP: Clock cycles between row precharge and activate
   Most motherboards for the first revision of the socket support solely DDR4 memory, a lesser number support DDR3(L) memory, and the least number have slots for both DDR4 or DDR3(L) but only one memory type can be installed. Some have UniDIMM support, enabling either type of memory to be placed in the same DIMM, rather than having separate DDR3 and DDR4 DIMMs. The second revision socket motherboards support only DDR4 memory.
   BULLET::::- Memory Clock: 400 MHz (BFG Technologies 6200 OC 410 MHz, PNY and EVGA 533 MHz)
  
  BULLET::::- Pixel Pipelines: 4
  
  BULLET::::- Memory: 256 (BFG Technologies 6200 OC PCI and EVGA e-Ge-Force 6200 PCI) / 128 (BFG Technologies 3DFuzion GeForce 6200 PCI) MB DDR on a 64-bit interface
  
  Section::::GeForce 6100 and 6150 series.
   The DDR3U (DDR3 Ultra Low Voltage) standard is 1.25 V and has the label "PC3U" for its modules.
  
  JEDEC Solid State Technology Association announced the publication of JEDEC DDR3L on July 26, 2010.
  
  Section::::Standards with similar names.
  
  Section::::Standards with similar names.:LPDDR3.
  
  LPDDR3 (Low Power DDR3) is a mobile DDR SDRAM standard, designed for mobile computing, and shares little in common with DDR3 memory – except maybe the maximum data rate.
  
  Section::::Standards with similar names.:GDDR3.
  
  GDDR3 (Graphics DDR3) memory, sometimes incorrectly referred to as "DDR3" because of its similar name, is an entirely different SDRAM standard designed for use in graphics cards.
   Performance for Java ME applications and games are slow than BREW. For 3D games, Java ME uses JSR 184 (M3G), which 3D games that are developed on Java ME are slower (which results in 10 frames per second on some/most handsets) and have limited graphics, while BREW uses either software rendering (if the BREW handset doesn't have a 3D acceleration chip) or OpenGL ES (which it can take advantage of its performance).
  
  Some/few handset manufacturers do not allow to integrate Java ME's virtual machine on a few of their phones.
   Internal banks are increased to 16 (4 bank select bits), with up to 8 ranks per DIMM.
  
  Protocol changes include:
  
  BULLET::::- Parity on the command/address bus
  
  BULLET::::- Data bus inversion (like GDDR4)
  
  BULLET::::- CRC on the data bus
  
  BULLET::::- Independent programming of individual DRAMs on a DIMM, to allow better control of on-die termination.
  