RAM Wars: Return of the JEDEC

Dueling Channels

DDR400 will offer dual memory channels that memory makers say will match the data rates of 800 MHz front-side bus chipsets.

During the coming weeks, Intel will launch its Springdale chipset with DDR400, which will represent the first commercially available dual channel memory application.

Dual channel memory is anything but new. It has been used for many years in servers and in Rambus memory and allows the memory controller, as it links to the memory module, to split the data and simultaneously write to one physical module on the right and one on the left.

Springdale will combine DDR400 with an 800 MHz P-4. At first glance, the P-4 800 MHz memory bus will be twice the speed of the 400 MHz DDR400, which would normally slow things down at a 400 MHz clock speed. Ideally, you would want to match the processor front side bus and the memory bus, so 800 MHz DDRAM would represent a perfect match in this hypothetical example.

But dual channel DDR400, in theory, offers the same bus speed as single-channel 800 MHz DDRAM.

Dual channel DDR400 requires two DIMM slots and two modules. The architecture, while offering 6.4 GBytes/s of peak bandwidth, simultaneously splits the back-and-forth signaling with the CPU. The signal from each channel comes from one of the two sockets in the DIMM slots.

Vendors are scrambling to offer chipsets that conform to DDR400. According to Crucial Technology, the following chipsets will support DDR400:

• Intel Processors with VIA P4X400, ALI M1681, SIS 648DX, or Intel Springdale;
• AMD Processors with KT400, SIS 746DX or 746FX, or Nvidia Nforce2.