NVIDIA GeForce 256 DDR

by Anand Lal Shimpi on December 25, 1999 7:23 PM EST

Why is the memory bandwidth of the GeForce a limitation? When its memory is running at its default clock of 166MHz, the GeForce has an available 2.7GB/s of memory bandwidth. While this is a large amount of available bandwidth, as the resolution and color depth of any particular application or game increase, so does the amount of memory required to render that particular scene. As you begin to saturate the GeForce's memory bus, you will notice a large drop in frame rate. The best way to illustrate this is by comparing the performance of a GeForce running at default clock in Quake III Arena at 16-bit and 32-bit color depths at 1024 x 768.

As you can see by the above graph, the performance difference is definitely noticeable. Now compare this to the performance drop at 640 x 480 when switching from 16-bit color to 32-bit color modes under Q3A, and we see much less of a drop, since at 640 x 480, the memory bandwidth requirements are significantly less than at 1024 x 768 (the higher the resolution, the more memory is needed).

There are a number of solutions to this problem, but only a few are practical. You could always increase the memory bus width to 256-bits, but that isn't very realistic because it is a significant change in the architecture of the chip. The tweaker's method of getting around this problem is by simply purchasing a GeForce with faster memory and overclocking the memory bus to higher levels, such as 183MHz or 200MHz. If you are lucky enough to have a GeForce board with 5ns SDRAM, then increasing your memory frequency to 200MHz on your GeForce will increase the available memory bandwidth to 3.2GB/s, an increase of 11% from a regularly clocked GeForce.

The more elegant solution is to use a memory technology that inherently offers greater bandwidth than conventional SG/DRAM. One technology in particular, Double Data Rate SG/DRAM, is capable of effectively doubling the memory bandwidth without significantly altering the design of the card itself. By transferring on both the rising and falling edges of the clock (normally transfers only occur on the rising edge of the clock), DDR SDRAM (and DDR SGRAM), while operating at a frequency of 150MHz, for example, can effectively transfer data as if the clock frequency were twice that, or 300MHz.

So, with a simple switch of memory types, the GeForce's memory bandwidth rockets from 2.7GB/s to an unparalleled 4.8GB/s*, which gives the GeForce a healthy boost in high resolution scenarios, so, without further ado, let's get to the benchmarks of a GeForce 256 equipped with DDR SDRAM.

*150MHz x 2 x 16-byte memory bus width = 4.8GB/s

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