More 925X: DDR2 and the new ICH

DDR2 Memory

The second important development is DDR2 memory support, exclusive in the case of Intel’s 925X. Motherboards based on either of the two 915 chipsets may support either conventional DDR or the new DDR2 modules.

What are the benefits of a new memory standard, you ask, especially if the front-side bus speed remains unchanged? That’s a good question, and to be frank, DDR2, even at 533MHz with 4.3GB per second of bandwidth, won’t make a perceptible difference in most applications. The most likely beneficiary at this point would probably be the integrated graphics core included with Intel’s 915G chipset.

DDR2 employs on-die termination, lower operating voltages, and a different signaling scheme in its endeavor to achieve better performance. As a result, it runs at faster frequencies – 533 and 400MHz today, hitting 667 and 800MHz in the future.

Unfortunately, a couple of caveats accompany the clock speed improvements associated with DDR2. The first is higher latencies – our 533MHz modules are rated at CAS4, an obvious detriment to usable throughput. Moreover, they are not backwards compatible with the standard 184-pin DDR slot, again necessitating a hardware purchase.

Intel is making special concessions to improve memory performance on the 925X. Although the actual implementation is somewhat obscure (Intel’s 925X presentation cites minimized latencies through memory access optimizations and maintenance commands), we’re looking at an equivalent to the PAT (performance acceleration technology) used on the familiar 875P chipset. Purportedly, Intel also learned a lesson from the motherboard manufacturers that used PAT on their 865 boards, and has taken steps to make sure 915P boards don’t emerge with the memory optimization technology.

ICH6

Amidst VIA’s V-Link, SiS’ MuTIOL, and NVIDIA’s single-chip nForce3, Intel’s 266MB per second hub interconnect was looking fairly outmoded, especially as fresh south bridge technologies gobble up additional bandwidth. Intel is finally responding with its DMI interface, which boasts 2GB per second, full duplex, to satiate the technologies introduced with its latest ICH6.