While there have been many reviews on DDR2, I fear early reviews for the new standard were unconsciously prejudicial. Many clankingly presumed DDR2 would; "pick up, where DDR1 left off," in speed and therefore performance. Truth is DDR2 is faster, so much so motherboards must run the higher speed modules on a divider, the asynchronous results of which were disappointing compared to its predecessor DDR1 due to high latencies associated with the speed.
In order for the memory we’re testing today to run at speed and synchronously with the processor's FSB, we would have to raise the CPU FSB speed to 336MHz. Even in an extreme overclocking environment this would be asking a lot from any CPU.
Luckily, motherboard makers such as Asus can help us reach this goal. It seems Intel programmed a 14x multiplier at boot up in their newest CPU’s, and with an overclocking BIOS such as Asus’s “Lock Free
" , you are able to change the multiplier on Pentium 4 CPU's from 530 to 570J (S775), as well as Prescott for S478 from 3.2E to 3.4E effectively transforming them into P4 520's or 2.8E's.
Intel is now becoming a victim of its decision to differentiate between low- and mid-end Pentium 4 Prescott's on the one hand and the more demanding versions at maximum clock speeds on the other. The so-called performance requirement bit or PRB (MSR_PLATFORM_BRV bit 18) is responsible for approving the usage of the processor's designated multiplier or a factory default one (which is x14). The latter was implemented for security reasons, as the requirements as well as thermal specifications of the two fastest P4s are much higher than for the mainstream models.
Our test today with Corsair
’s DDR2 modules will focus on getting up to speed with this new standard (DDR2 667), and to exemplify any performance differences running the system off the lower multiplier, and attempting a straight overclock.
The benefits of DDR2 are slowly beginning to emerge as more and more End-users begin to purchase systems and familiarize themselves with this new standard. Unfortunately current PCIe motherboards are limited in their BIOS options and it's been quite the debacle. A conundrum exists in the given ability to lower the multiplier for higher FSB speeds, yet to there's no option for locking the PCIe graphics bus. The good news dispelling initial claims there was an overclocking ceiling at just 10%, can be safely laid to rest. I commend Intel Fabs, as .09-micron yields of both 478 pin and S775 BGA packaged P4's has been outstanding. I've had three of these processors including the Socket 478 3.0E, S775 P4 530 and P4 550, all overclocked a minimum of 600Mhz without a need to increase Vcore. With relatively small Vcore increases all have ran at or above 4.0GHz. Of the three, I'm most impressed with my P4 550 which easily overclocks beyond its native 3.4GHz (200FSB) to 4.0GHz (240FSB) without any increase in Vcore.
Problems begin to occur at 250FSB, however; this is primarily attributable to the absence of a PCIe lock. With the PCIe bus unlocked, at 260FSB the graphics card is running from a 120MHz bus speed. Prima facie these figures may appear benign, and while the new PCIe bus leaves Sideband Addressing
by the wayside overclocking the graphic card this high can become problematic, eventually damaging the card. The inability to lock the PCIe bus becomes pertinent as we try to run our DDR2 667 at specified speed. While it's exciting to have such high speed memory, it's equally agitating if you’re unable to exploit the memory's full potential due to seemingly “simple” BIOS and motherboard deficits.
Onto our test setup ->