Specifications

Video Display Adapters
903
Video RAM
Most video adapters rely on their own onboard memory that they use to store video images while
processing them; although the AGP specification supports the use of system memory for 3D textures,
this feature is seldom supported now that video cards routinely ship with 32MB, 64MB, or more of
onboard memory. Many low-cost systems with onboard video use the universal memory architecture
(UMA) feature to share the main system memory. In any case, the memory on the video card or bor-
rowed from the system performs the same tasks.
The amount of memory on the adapter or used by integrated video determines the maximum screen
resolution and color depth the device can support. You often can select how much memory you want
on a particular video adapter; for example, 32MB, 64MB, and 128MB are common choices today.
Although adding more memory is not guaranteed to speed up your video adapter, it can increase the
speed if it enables a wider bus (from 64 bits wide to 128 bits wide) or provides nondisplay memory as
a cache for commonly displayed objects. It also enables the card to generate more colors and higher
resolutions and, for AGP cards (see the following), allows 3D textures to be stored and processed on
the card, rather than in slower main memory.
Many types of memory have been used with video adapters. These memory types are summarized in
Table 15.11.
Table 15.11 Memory Types Used in Video Display Adapters
Memory Relative
Type Definition Speed Usage
FPM DRAM Fast Page-Mode RAM Slow Low-end ISA cards; obsolete
VRAM
1
Video RAM Fast Expensive; obsolete
WRAM
1
Window RAM Fast Expensive; obsolete
EDO DRAM Extended Data Out DRAM Moderate Low-end PCI-bus
SDRAM Synchronous DRAM Fast Low-end PCI/AGP
MDRAM Multibank DRAM Fast Little used; obsolete
SGRAM Synchronous Graphics DRAM Very fast High-end PCI/AGP; replaced by DDR SDRAM
DDR SDRAM Double-Data Rate SDRAM Very fast High-end AGP
DDR-II SDRAM DDR SDRAM, 4-bit per- Extremely fast High-end AGP, PCI Express
cycle memory fetch
GDDR-3 Modified DDR SDRAM Extremely fast High-end AGP, PCI Express
SDRAM
1. VRAM and WRAM are dual-ported memory types that can read from one port and write data through the other
port. This improves performance by reducing wait times for accessing the video RAM compared to FPM DRAM and
EDO DRAM.
Note
To learn more about memory types used on older video cards (FPD DRAM, VRAM, WRAM, EDO DRAM, and MDRAM),
see Chapter 15 of Upgrading and Repairing PCs, 12th Edition, available in electronic form on the disc packaged with
this book.
SGRAM, SDRAM, DDR, and DDR-II SDRAM—which are derived from popular motherboard memory
technologies—have replaced VRAM, WRAM, and MDRAM as high-speed video RAM solutions. Their
high speeds and low production costs have enabled even inexpensive video cards to have 16MB or
more of high-speed RAM onboard.
Chapter 15
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