Hardware Reference
In-Depth Information
VRAM and WRAM
VRAM and WRAM 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 VRAM compared to FPM DRAM and EDO DRAM.
SGRAM
SGRAMwasdesignedtobeahigh-endsolutionforfastvideoadapterdesigns.SGRAMis
similartoSDRAMinitscapabilitytobesynchronizedtohigh-speedbusesupto200MHz,
but it differs from SDRAM by including circuitry to perform block-writes to increase the
speed of graphics fill and 3D Z-buffer operations.
DDR SGRAM
DDR SGRAM is designed to transfer data at speeds twice that of conventional SGRAM
by transferring data on both the rising and falling parts of the processing clock cycle.
GDDR2 SGRAM
There have been several variations of what has been called GDDR2. The first was based
on standard 2.5V DDR SDRAM with some enhancements, whereas the second was actu-
ally based on 1.8V DDR2 SDRAM, and with much higher performance and cooler oper-
ation.
GDDR3 SGRAM
GDDR3 SGRAM is based on DDR2 memory, but with two major differences:
• GDDR3 separates reads and writes with a single-ended unidirectional strobe, whereas
DDR2 uses differential bidirectional strobes. This method enables higher data transfer
rates.
• GDDR3 uses an interface technique known as pseudo-open drain, which uses voltage
instead of current. This method makes GDDR3 memory compatible with GPUs de-
signed to use DDR, GDDR2, or DDR2 memory. To determine the type of memory
used on a particular video card, check the video card manufacturer's specification
sheet.
GDDR4 SGRAM
Some of the newer cards use GDDR4 SGRAM. Compared to GDDR3, GDDR4 memory
has the following features:
•Higherbandwidth.GDDR4runningathalfthespeedofGDDR3providescomparable
bandwidth to its predecessor.
