NVIDIA GeForce 256 Part 1: To buy or not to buyby Anand Lal Shimpi on October 11, 1999 5:07 PM EST
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The memory bus is still 128-bits wide and operates at a default clock of 166MHz. Basic math will tell us that this results in around 2.6GB/s of local memory bandwidth on a regularly clocked GeForce 256 card. If you're familiar with the fastest graphics cards from the previous product cycle, (i.e. TNT2, G400) you'll know that with a memory clock of 166MHz, the amount of memory bandwidth the GeForce 256 offers is noticeably lower than the G400MAX and even the TNT2 Ultra. While the GeForce 256's 2.6GB/s of memory bandwidth is greater than the 2.4GB/s of a regular TNT2, it is less than the ~2.9GB/s of the TNT2 Ultra and definitely less than the 3.2GB/s provided for by the 200MHz memory clock of the G400MAX.
Our review sample GeForce 256 came outfitted with 5ns memory chips which results in a theoretical maximum memory clock of 200MHz, much higher than the 166MHz NVIDIA rated it at. At the same time, many video card manufacturers (i.e. Leadtek) have already announced that they will be shipping GeForce 256 cards with 5ns memory. A handful of others will be using 5.5ns (183MHz) memory which will at least bring up the amount of available bandwidth to TNT2 Ultra levels. So why would NVIDIA set the memory clock so low?
The first possibility that comes to mind is to keep the overall cost of the boards low. The 23 million transistor GeForce 256 is a costly part to produce and there is very little cost that can be saved there as long as the fabrication process stays at 0.22-micron, so one of the obvious areas to cut costs in would be memory. This will enable manufacturers of 'vanilla' GeForce 256 cards that adhere entirely to NVIDIA's spec to keep their prices low by using slower 6ns memory chips. At the same time, this opens up a new avenue for hardcore gamer GeForce 256 boards that feature faster memory chips and sell at a higher premium.
Just recently, the topic of using Double Data Rate SDRAM or SGRAM on a GeForce 256 board was brought up with the announcement of DDR GeForce 256 boards from Creative Labs, Guillemot, and Leadtek. Double Data Rate (DDR) SDRAM/SGRAM has been around for quite some time and is theoretically a very intelligent solution that offers a low latency and a greater memory bandwidth. The way DDR SDRAM/SGRAM works is that it transfers data on both the rising and falling edges of the clock like the AGP bus, therefore doubling the amount of available memory bandwidth. This way, NVIDIA can boast that their 128-bit memory bus offers just as much bandwidth as Matrox's Dual 128-bit bus or as a 256-bit memory bus.
At the current memory clock speed, using DDR SDRAM on a GeForce 256 would result in an amazing 5.2GB/s of memory bandwidth, and at 200MHz (5ns chips) it would offer 6.4GB/s. This would come in handy particularly in 32-bit color rendering modes and at high resolutions when a considerable amount of memory is required.
Unfortunately, there is a downside to all of this. Currently, DDR SDRAM/SGRAM is very rare and it will continue to be rare for quite some time. The chances of picking up a GeForce 256 this year with DDR memory on it is next to nothing and the first signs of publicly available DDR models will probably be sometime next year. Samsung recently announced their DDR SDRAM chips but for now they are out of the reach of the mass market, making our conventional SDRAM/SGRAM (also referred to as Single Data Rate - SDR) the choice for most GeForce 256 boards.