Chapter 12: Video Cards^267
Double Data Rate SDRAM (DDR SDRAM) DDR SDRAM doubles the data
rate of standard SDRAM to produce faster data transfers. DDR memories are
becoming more commonplace on video cards, especially 3D video accelerators.
Synchronous Graphics RAM (SGRAM) An improvement on SDRAM
that supports block writes and write-per-bit, which yield better graphics
performance. Found only on video cards with chipsets that support these
features, such as many Matrox video cards. SGRAM is a single-ported
memory technology.
Double Data Rate SGRAM (DDR SGRAM) DDR SGRAM is showing
up on the very latest cards. It doubles the data rate of SGRAM and offers
better performance.
Direct Rambus DRAM (RDRAM) A newer general-purpose memory type,
also being used on video cards, which includes bus mastering and a dedicated
channel between memory devices. RDRAM runs about 20 times faster than
conventional DRAM.See Chapter 5 for more information on memory technologies.Bus Mastering
BusmasteringallowsthevideocardtocontrolthePC’ssystembusandtransferdataintoand
out of system RAM directly without the assistance of the CPU. This improves the perfor-
mance of certain video operations that use RAM for calculations, such as 3D acceleration.Video Chipsets
The logic circuits that control the video card’s functions are grouped together as the
video card’s chipset, which is also called the graphics chip, the accelerator, or the video
coprocessor. Much like the functions performed by the system chipset on the mother-
board, the video chipset supports all of the functions performed by the GPU, as well as
the interfaces, data transfers, and compatibility of the card.
Some video card manufacturers make their own video chipsets, such as Matrox and
3dfx, who design and build their cards from start to finish; others use chipsets manufac-
tured by other companies, such as Diamond Multimedia. The video chipset is important
because it holds the key to the card’s performance, capabilities, and compatibility.
Animportantfeaturecontrolledbythevideochipsetisthevideocard’srefreshrate.A
higher refresh rate means less flicker on the screen, which translates to less eyestrain for
the user. A good video chipset should provide a refresh rate of at least 75Hz. However,
the refresh rate must be balanced to the resolution settings. Using a higher resolution set-
ting should result in a lower refresh rate, and vice versa.