Video RAM Technology Types

Today's video cards are high bandwidth cards that need every performance boost to accommodate high resolutions and refresh rates along with fast performance. System DRAM needed to be pushed aside for faster, more specialized breeds of memory.

Video RAM - VRAM

VRAM is a form of FPM DRAM made specifically for Video Cards, with one additional feature: dual ports. This allows the RAMDAC and CPU to access Video Memory simultaneously regardless of each other. It is rarely used nowadays as SGRAM is considerably cheaper to produce.

Windowed RAM - WRAM

WRAM is an advanced form of VRAM that is not coincidentally expensive, as well. It shrinks the footprint of the dual ports while adding EDO features that accelerate functions used often on Microsoft's Windows 9x platform. It is also cheaper to produce than VRAM, but not enough to justify a switch from SGRAM.

DRAM - FPM/EDO/SD

These forms of Video memory are no different than their system RAM counterparts, with the exception of faster access times. Better engineering technology has kept EDO DRAM alive, in particular by efforts from Silicon Magic, which makes the EDO DRAMs with SDRAM level latency necessary for 3Dfx Interactive's Voodoo line of 3D Accelerator cards.

Synchronous Graphics RAM - SGRAM

Another new form of video memory is SGRAM. It doesn't offer the extreme performance of VRAM's dual ports, but makes up for it with SDRAM technology and specific graphic memory functions (such as block writing). SGRAM is slightly more expensive than SDRAM but provides the necessary performance for CAD level video cards.

Multibank DRAM - MDRAM

With most RAM, data must be written sequentially - the I/O port can only allow so much at a time, sort of like driving through the entrance of a parking garage. Multibank DRAM solves this by using a large array of individual 32 kilobyte DRAM banks, each with their own I/O port. This allows memory to be read/written to/from in multiple areas simultaneously. It also allows card manufacturers to use exact numbers of memory (odd numbers like 2.5 megabytes).

Cached DRAM - CDRAM

This alternative technology is hybrid of stable SRAM combined with DRAM. By integrating small areas of 15 ns static ram into each DRAM chip, primary accesses can be made much faster. Mitsubishi has taken this technology to another level with 3DRAM.

Enhanced DRAM - EDRAM

Like CDRAM, Enhanced DRAM uses 15 ns SRAM integrated into DRAM chips, but the differences end there. EDRAM uses the SRAM in a direct mapped approach (slower than CDRAMs set associative method), but manages to use 35 ns DRAM (twice as fast as CDRAM). www.mitsubishi.com

Integrated DRAM - IDRAM

Instead of making DRAM parts, some engineers decided 'why not just throw it all on the microprocessor chip?', and that's just what this technology does. By putting the memory directly on the die, bandwidth can be as high as the designer wants without concerns about engineering costs. IDRAM technology is considered mostly for the notebook market, because integrated memory results in up to 60% less power use.

3DRAM / 3DRAMX

Mitsubishi decided to take the idea of integrated memory the other way, and came up with the most powerful video RAM today - 3DRAM. Instead of putting the memory in the microprocessor, the microprocessor is put in memory! An ALU on chip accelerates Z-Buffering and Alpha Blending, while on-chip SRAM provides faster seek times - the same way CDRAM is used.

There are 4 different levels of 3DRAM, each successive number bringing faster ALUs and more features on board the silicon.

How much RAM do I need for my video card?

The exact amount of RAM you need depends on your resolution (width x height to determine the exact number of pixels used) multiplied by your color depth (the total amount of colors supported). 8 bits equals one byte, and each pixel also uses a byte for location. This amount of data is called the "Frame Buffer".

32bit Modes: There is one 32bit mode - but it doesn't use the same formula. It combines 24-bit color with an "alpha" channel which allows for 256 layers of transparency.

Video Cards are not limited to the Frame Buffer for memory use though. Many games are double or triple buffered, which requires double or triple the space as you would think! Also, 3D games use textures, which when counted up far exceed the RAM capacity. Larger ram amounts help keep the card from retrieving textures from the hard disk or system memory.

When looking at RAM levels on video cards, keep in mind what you need it for. PhotoShop users may feel content with 8 megabytes (to use 1600x1200 mode), but 3D modelers will feel more at home with 16-32 megabytes (to cover high resolutions plus triple buffering).

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