First EPP DIMM sets memory speed record

CORSAIR, one of the leaders in "performance enhanced" high end memory for overclockers and other "enthusiasts" has again outsmarted competitors like OCZ or Crucial by shipping the very first real, guaranteed DDR2-1066 (PC8500) memory out there.

Its PC2-8500 TwinX 1 GB (2 x 512MB DIMM) set provides this rated speed, synchronous with the 1066 MHz FSB of "Extreme" Presler Pentiums and mainstream Conroes.

These are also the first kits I know of that support the new EPP enhanced performance extension for the DIMM SPDs, as will most of the overclocker's memory in the future - EPP extends the SPD concept to include extra configuration info for highest-performance settings at higher voltages for automatic top-speed detection by the memory controller.

PC1066 is expected to be the last major DDR2 frequency milestone before DDR3 takes over the performance lead next year. But, is it on any use on the current boards, and how does it compare against its elder brethren? I ran the memory on two boards, one the Intel 975XBX, my standard Presler reference, with 4.26GHz dual-core setup, but limited to DDR2-800 memory speeds - it runs the Corsair 5400UL memory at DDR2-667 CL3-2-2-7 at 1.9 V, a very low latency ideal for in sync work with future Conroe XE 1333MHz FSB; the other one being ASUS P5WD2-E, also a 975X board but with memory overclocking capability to run in DDR2-1066 mode. It also ran Presler XE CPU, but only at 3.73GHz. The 4.26GHz operation was, for some reason, unstable on this board.

Interesting results! I simply plugged out the well-performing 5400UL modules, without changing the tuned BIOS settings, hoping that, after plugging in the newer DDR2-1066 ones, the same (or hopefully) better settings would work. Well - no! It didn't work at DDR2-667 CL 3-2-2-7 or DDR2-800 CL 4-3-3-9, both at 1.9 volts, neither did it work at DDR2-533 CL 3-2-2-6 at 1.8 volts. In all of these settings, both the 1 year old Corsair 5400UL, and 6 month old 8000UL, work perfectly across a range of Intel boards. I had to reduce the latency to CL 4-4-3-10 go get it to work at DDR2-800, and CL 3-3-2-8 at DDR2-667, both at 1.9 volts. At 2.1 volts, however, the situation improved: I did get CL 4-3-3-9 at DDR2-800, and CL 3-3-2-7 at DDR2-667.

On the Asus, however, I managed to get 5-5-4-12 at DDR2-1066, in sync with the CPU FSB. In fact, since it's dual channel operation, the memory bandwidth is exactly twice the CPU bandwidth. So, I ran the memory in two modes, both in sync with CPU FSB: DDR2-533 at CL 3-2-2-6 1.9 v, and DDR2-1066 5-5-4-12 at 2.1 v. Since both modes fully satisfy the CPU FSB bandwidth, and are synchronous to it, the results should be similar - how much use is the extra DDR2-1066 bandwidth? Here are the Sandra results:

Sandra 2005	533MHz	800MHz	1066MHz
Integer	6610MB/s	6754MB/s	6912MB/s
Floating Point	6593MB/s	6746MB/s	6903MB/s

As you can see, there IS a benefit to using DDR2-1066 memory, probably due to the faster burst transfer completion. Even if the first word latency is same, the subsequent word transfers will only take half the time due to twice the clock, helping those 8-word prefetches. Keep in mind it comes at the price of higher voltage (creating more heat and power dissipation, and of course, DDR2-1066 DIMMs aren't cheap either.

What would I look for here? I hope Corsair can fix the latency a bit, like bring it down to say 5-4-4-10 at 1066 speed, and, even more important, we need the 2 x 1 GB DIMM pair too. OCZ did make some interesting noises in this direction, trying to get a DDR2-1100 part out, but let's see - for now, if you want a pair of 512MB DIMMs that gets the most out of your FSB1066 Intel CPU, Corsair's got the stuff. µ