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Taking the PC RAM One Letter Further

July 08, 1996|RICHARD O'REILLY

Q: Could you explain the differences between VRAM, WRAM and RAM as they are used for graphics?

--Paul Goldsmith


A: RAM is actually a generic term that can cover several kinds of random access memory. To review, all kinds of RAM can store whatever information is required at any time. It contrasts with ROM, or read-only memory, which has its contents permanently embedded.

The most common--and least expensive--kind of RAM is DRAM, or dynamic random access memory. It is the kind of RAM that is usually being referred to when you see "RAM" in articles or advertisements.

What makes it "dynamic" is actually a weakness. It can't store information for longer than an instant or so, forcing the computer to constantly update, or "refresh," the content.

A different, much faster and much more expensive kind of RAM is SRAM, or static random access memory. It doesn't need refreshing, making it an ideal kind of memory for storing data on a microprocessor.

With the advent of high-resolution color graphics, video adapters have run up against a big limitation of DRAM: It works like a one-way street. But video adapters have a two-way task. They not only have to receive the data to be displayed on the screen, they also have to constantly repaint the screen. The higher the resolution, the faster it has to be repainted.

IBM Corp. publishes an interesting application note for engineers designing graphics boards. It shows that a DRAM system has only about 40% of its capacity left to receive data updates because it is so busy sending pixels to the screen.

VRAM, for Video RAM, and WRAM, for Windows RAM, are two approaches to curing the DRAM limitation. Both are two-way RAM chips that can simultaneously feed the computer monitor's incessant demand for pixels to display and receive data from the microprocessor. Of course, VRAM costs more than DRAM.

WRAM, a dual-port RAM chip from Samsung, is about 20% cheaper than VRAM and is faster, according to Matrox Electronic Systems Ltd., which uses WRAM instead of VRAM in its high-performance graphics board.

Users of traditional key-stroke oriented business software like word processing, database and spreadsheets can get by just fine with inexpensive DRAM-based graphics cards. But people doing high-end graphics, such as design and photo manipulation, or those who play high-speed graphics-intensive games will see a big difference by investing in VRAM or WRAM-based graphics adapters.

Richard O'Reilly, The Times' director of computer analysis, will answer questions of broad interest in this column. E-mail questions to cutting; fax to (213) 237-4712; or mail to Answers c/o Richard O'Reilly, Business Section, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053.

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