Video Hardware - Upgrading and Repairing PCs - page 775

a multicard solution that allows you to use two or more PCIe video cards to increase your
graphics processing performance.
See “ Dual-GPU Scene Rendering ,” p. 637 (this chapter).
Note
If your system uses integrated graphics and you have less than 2GB of RAM, you might
be able to increase your available graphics memory by upgrading system memory (system
memoryisusedbytheintegratedchipset).SomeIntelchipsetswithintegratedgraphicsauto-
matically detect additional system memory and adjust the size of graphics memory automat-
ically.
Video Memory Bus Width
Anotherissuewithrespecttothememoryonthevideoadapteristhewidthofthebuscon-
necting the graphics chipset and memory on the adapter. The chipset is usually a single
largechiponthecardthatcontainsvirtuallyalltheadapter'sfunctions.Itiswireddirectly
to the memory on the adapter through a local bus on the card. Most of the high-end ad-
aptersuseaninternalmemorybusthatisupto512bitswide(ormoreinsomecases).This
jargon can be confusing because video adapters that take the form of separate expansion
cards also plug into the main system bus, which has its own speed rating. When you read
about a 256-bit, 384-bit or 512-bit video adapter, you must understand that this refers to
the memory connection on the card, not the connection to the motherboard. In two cards
with otherwise similar GPU, memory type, and memory size specifications, the card with
the wider memory bus is preferable because a wider memory bus boosts performance.
See “ System Bus Types, Functions, and Features , ” p. 233 ( Chapter 4 , “ Motherboards
and Buses ” ).
The DAC
The DAC (or RAMDAC) does exactly what its name describes. The RAMDAC is re-
sponsible for converting the RAM-based digital images your computer generates into sig-
nalsforanalogmonitorconnections.ThespeedoftheRAMDACismeasuredinMHz;the
faster the conversion process, the higher the adapter's vertical refresh rate. The speeds of
the RAMDACs used in today's high-performance video adapters range from 300MHz to
400MHz. Most of today's video card chipsets include the RAMDAC function inside the
3D accelerator chip, but some dual-display-capable video cards use a separate RAMDAC
chiptoallowtheseconddisplaytoworkatdifferentrefreshratesthantheprimarydisplay.
Systems that use integrated graphics include the RAMDAC function in the North Bridge
or GMCH chip portion of the motherboard chipset.