The basic idea behind DDR SDRAM is that you take a normal SDRAM module and redesign it to be able to send data on the rising and falling edge of each clock. Instead of running the SDRAM twice as fast, which is an exceedingly difficult task, you enable it to send data twice as fast, a less difficult task, thereby providing about twice the theoretical maximum memory bandwidth.

There are two current forms of DDR system memory running around, each with a variety of interesting names. The first is DDR1600, a.k.a. DDR200. DDR1600/DDR200 runs at 100MHz DDR, with the equivalent of 200MHz of bandwidth. On a 64-bit wide memory bus, the standard for today's SDRAM desktop systems, DDR1600/DDR200 provides a theoretical peak of 1600MBps of memory bandwidth, hence the name DDR1600. We must admit, we are not fans of the new memory naming convention. It seems to have more hype than substance.

The second is DDR2100, a.k.a. DDR266. DDR2100/DDR266 runs at 133MHz DDR, with the equivalent of 266MHz of bandwidth. On a 64-bit wide memory bus, DDR2100/DDR266 provides a theoretical peak of about 2100MBps of memory bandwidth, hence the name DDR2100.

The Tyan Trinity A762 motherboard we used sported 128MB of Micron PC1600 DDR SDRAM in one of its four slots. This matches up on bandwidth with the 1600MBps of the 200MHz FSB of the Athlon Thunderbird 1.1GHz we used for testing. You will likely need to have a 266MHz FSB Athlon Thunderbird or Duron in order to use DDR2100 memory with the AMD 760 chipset.

The future of DDR is not yet set, though the development process is in motion. Over the mid-term, motherboards with DDR chipsets will hit the market in late 2000 and early 2001, and will likely quickly move into the volume lead for performance desktop systems. Tyan's performance oriented board is likely representative of what will come out early on -- high-performance boards that will cost somewhere under $200.

Whether the final performance of DDR is faster, slower, or the same as that of RDRAM, we have little doubt that DDR memory will replace SDR memory as the choice for system memory over the next couple of years. RDRAM will likely not see the volumes DDR SDRAM will see any time soon.

As for the future of DDR clock speeds, we expect them to rise relatively quickly as far as memory speeds go. While DDR is starting at 200MHz for system memory, it will quickly transition to 266MHz, and 333MHz is not far ahead.