Specifications

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Chapter 15 Video Hardware
SDRAM
Synchronous DRAM (SDRAM) is the same type of RAM used on many current systems based on proces-
sors such as the Pentium III, Pentium 4, Athlon, and Duron. The SDRAMs found on video cards are
usually surface-mounted individual chips; on a few early models, a small module containing SDRAMs
might be plugged into a proprietary connector. This memory is designed to work with bus speeds up to
200MHz and provides performance just slightly slower than SGRAM. SDRAM is used primarily in cur-
rent low-end video cards and chipsets such as NVIDIA’s GeForce2 MX and ATI’s RADEON VE.
SGRAM
Synchronous Graphics RAM (SGRAM) was designed to be a high-end solution for very fast video
adapter designs. SGRAM is similar to SDRAM in its capability to be synchronized to high-speed buses
up to 200MHz, but it differs from SDRAM by including circuitry to perform block writes to increase the
speed of graphics fill or 3D Z-buffer operations. Although SGRAM is faster than SDRAM, most video
card makers have dropped SGRAM in favor of even faster DDR SDRAM in their newest products.
DDR SDRAM
Double Data Rate SDRAM (also called DDR SDRAM) is the most common video RAM technology on
recent video cards. It is designed to transfer data at speeds twice that of conventional SDRAM by trans-
ferring data on both the rising and falling parts of the processing clock cycle. Today’s mid-range and
low-end video cards based on chipsets such as NVIDIA’s GeForce FX and ATI’s RADEON 9xxx series use
DDR SDRAM for video memory.
DDR-II SDRAM
The second generation of DDR SDRAM fetches 4 bits of data per cycle, instead of 2 as with DDR
SDRAM. This doubles performance at the same clock speed. The first video chipset to support DDR-II
was NVIDIA’s GeForce FX, which became the top of NVIDIA’s line of GPUs in late 2002. DDR-II (also
spelled DDR-2) is also used by ATI’s high-end graphics cards.
GDDR-3 SDRAM
GDDR-3 SDRAM, which began appearing on NVIDIA’s high-end graphics cards in early 2004, is based
on DDR-II memory, but with two major differences:
■ GDDR-3 separates reads and writes with a single-ended unidirectional strobe, whereas DDR-II
uses differential bidirectional strobes. This method enables much higher data transfer rates.
■ GDDR-3 uses an interface technique known as pseudo-open drain, which uses voltage instead of
current. This method makes GDDR-3 memory compatible with GPUs designed to use DDR or
DDR-II memory.
√√ For more information about DDR, DDR-II, and GDDR-3, see Chapter 6, “Memory.”
Video RAM Speed
Video cards with the same type of 3D graphics processor chip (GPU) onboard might use different
speeds of memory. For example, two cards that use the NVIDIA GeForce FX 5200—the Prolink
PixelView and the Chaintech A-FX20—use different memory speeds. The Prolink card uses 4ns mem-
ory, whereas the Chaintech card uses 5ns memory.
Sometimes, video card makers also match different memory speeds with different versions of the same
basic GPU, as with ATI’s Radeon 9800 XT and 9800 Pro. The 9800XT has a core clock speed of
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