[ The PC Guide | Systems and Components Reference Guide | Video Cards | Video Memory Technologies ]
Multibank DRAM (MDRAM)
A new type of memory that attempts to address two problems with conventional video
memory, Multibank DRAM or MDRAM was invented by MoSys specifically for use
in graphics cards. MDRAM differs substantially in design from other types of video memory.
Conventional memory designs use a single monolithic "block" of memory for the
frame buffer. MDRAM breaks its memory up into multiple 32 KB banks that can be accessed
independently. This provides the following advantages:
- Interleaving: Memory accesses can be interleaved between banks, allowing accesses
to overlap to provide greater performance. This has the effect of increasing performance
without the use of dual porting; the concept is similar to the use of interleaving for the
system memory on high-end chipsets.
- Flexibility in Memory Sizing: With conventional memory, it is only practical to
make video cards with whole megabytes of memory: you see cards with 1 MB, 2 MB, 4 MB etc.
of video RAM. This can cause a great deal of memory waste. For example, to run 1024x768
resolution in true color (24 bits) requires 2.25 MB of video memory for the frame buffer,
but a conventional video card would have to be outfitted with 4
MB of memory to support this mode. With MDRAM this restriction is removed and a card
can be created with exactly 2.25 MB if desired.
- No Size-Related Performance Penalties: In some conventional video card designs the access speed to the memory is related to the amount of memory used.
This means that a 1 MB DRAM card will run slower than a 2 MB one. This limitation does not
apply to MDRAM.
MDRAM is also cost-effective to manufacture compared to VRAM and is efficiently
organized to reduce waste. MDRAM is suitable for use in high-end applications and is
becoming popular due to its performance-enhancing and cost-reducing features. Its most
popular implementation is probably on the Tseng Labs ET6000 chipset, currently being used
by several card manufacturers.
 Next: Comparison of Video Memory Technologies
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