Desktop PCs


Which interfaces do I look out for?

The predominant interface on the motherboard used to connect graphics cards is PCI Express x16. Some motherboards may have two of these types of slots, which means that two graphics cards can be installed in unison. For NVIDIA-based cards, this is called SLI; while for ATI-based cards it's called CrossFire. A motherboard will only support one or the other, but not both. SLI and CrossFire are aimed at enthusiast users and hardcore gamers who want to have the most graphics processing power available to them. All new motherboards will ship with one PCI Express x16 slot, but only high-end motherboards will have two PCI Express x16 slots.


PCI Express

PCI Express, or PCIe, was ratified in late 2002 to overcome the limitations of AGP, which was the old graphics card interface that can't be found in new systems today. The PCIe interface has a higher bandwidth throughput than AGP, lower pin count and lower latency, making it a superior connection interface for graphics. .PCIe can be used not only for graphics cards, but for other add-in PC expansion cards, such as digital TV tuners and wireless networking cards. As such, there are currently four PCIe modes that can be found in today's PCs:

  • PCIe x1 mode (500MBps) uses a single data lane -- both directions
  • PCIe x4 mode (1000MBps) uses a double data lane -- both directions
  • PCIe x8 mode (4000MBps) uses a quadruple data lane -- both directions.
  • PCIe x16 mode (8000MBps) uses 4000MBps per directions.

Nearly all graphics cards are of the PCIe x16 variety.


Which memory?

Graphics cards also contain onboard RAM, which is used as a working space for the graphics operations.

The two graphics memory types you are likely to encounter are DDR3 (Double Data Rate) and DDR4 (this can be found in some high-end cards). Some budget cards also feature slower DDR2 memory.

A powerful graphics card will have up to 512MB of memory, while a mid-range card will have 256MB (but some can be found with 512MB) and budget cards can also be found with 256MB. A key specification is the memory bus, not just the memory capacity. Two cards that have the same memory capacity will perform differently if they have different sized memory buses. High-end cards can have a memory bus as wide as 512 bits, while mid-range cards have a 256-bit bus and budget cards can have a bus as narrow as 64 bits.

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