DDR Technology is Here
This content was originally featured on Amdmb.com and has been converted to PC Perspective’s website. Some color changes and flaws may appear.Anyone who has paid attention during the recent surge of video card advancements has at least heard of the DDR technology. The acronym for Double Data Rate, DDR is essentially this: the ability for data to be transmitted on both the rising and falling sides of a clock cycle. While this sounds confusing, it is actually quite simple to understand. On a standard bus, something running at 100 MHz, be it RAM or a CPU, can transmit and receive data once on each cycle. While on a EV6 DDR bus system, data can be transmitted on both ends of the cycle, giving the object that is running at 100 MHz the speed and bandwidth of a 200 MHz one.
Athlons have been using DDR since day one. Even the Slot A processors used a DDR bus. Each CPU, while running at a FSB of 100 MHz, had an effective FSB of 200 MHz due to Double Data Rate transfers. Video cards were the next major PC component to realize the potential in DDR SDRAM. The GeForce series of video cards were released in both a standard SDRAM format and a DDR format, and the improvement was extremely noticeable, to say the least. The NVIDIA GeForce cards used DDR SDRAM chips on the video cards, essentially doubling the amount of memory bandwidth they had to work with. And now this same DDR RAM is coming home to your PC.
DDR SDRAM comes in two flavors: PC1600 and PC2100. Both have corresponding bus speeds that take advantage of them. PC1600 is the memory speed for FSB100/DDR200 bus speeds and corresponds to a total available memory bandwidth of 1.6 GB/sec. The PC2100 memory is for FSB133/DDR266 bus speeds and gives us a bandwidth maximum of 2.1 GB/sec. Considering the PC133 memory gave us a bandwidth rating of 1.03 GB/sec, so PC2100 DDR is quite an enhancement. Keep in mind, that at least on paper, dual channel RAMBUS out does DDR by supplying 3.2 GB/sec of bandwidth.
A bit of a disappointment, the AMD760 chipset does not have a FSB/Memory bus adjustment to allow differential memory clocks like the KT133 chipset did. This feature in the KT133 chipset is what allowed us to have 100 MHz FSB and 133 MHz memory bus. This means, that until you get the FSB of your processor up to 133 MHz, you will not be able to enjoy the full benefits of PC2100 DDR SDRAM. If you are lucky enough to find one of the just emerging 133 MHz FSB Athlon processors, you could set the motherboard to a 133 MHz bus, therefore using the full FSB133/DDR266 memory bandwidth. Rumors have been circulating of VIA including the differential memory clock option in its forthcoming DDR chipset, which would allow users of the 100 MHz processors to fully utilize PC2100 DDR RAM.
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This picture shows the RAM we received with the Gigabyte 7DXC motherboard. It is a 128MB PC2100 RAM. I am unsure of the source of the memory, as I was unable to contact Gigabyte prior to the publishing of this article. The memory is an engineering sample and not available for sale, as of now. It’s 266 MHz DDR compatible and has CAS Latency of 2.5, which is different than the standard CAS 2 or 3 we see in standard SDRAM. While I am not positive on this next fact, the SDRAM chips serial numbers and marking indicated a 7.5ns speed on the RAM, as well.
The only noticeable physical difference between standard SDRAM and DDR SDRAM, is the placement and number of notches. Notice that DDR SDRAM only has one notch, which would prevent putting RAM in the wrong slots.