The JEDEC standard for DDR2 memory voltage is 1.8v, comparatively low when you consider the 2.5 to 2.9v required for most original DDR modules. The Crucial Ballistix requires a headier 2.2v to attain top performance, meaning you’ll need to make sure your motherboard supports voltages of 2.2v or over. During testing we found the memory to remain quite cool to the touch, so we expect the higher voltage to be perfectly safe for extended periods of time.
Test Rig
Asus P5WD2-E Premium Intel 975X Motherboard
Intel Pentium D 920 Processor
ATi Radeon X1900XTX Graphics
Seasonic S12-600 600watt PSU
To test the memory, we ran multiple passes of Memtest86+ v1.65 at each setting until we received errors. We then increased memory voltage and re-tested, repeating the process until we could raise vdimm no more.
The only memory we currently have for comparison is Corsair Value Select PC2-5300; not exactly a fair comparison, but useful none the less. The Crucial passed Memtest fine at its rated speed and timings, DDR2-800 4-4-4-12 with the processor front side bus at 266MHz. Something the Intel 975X chipset allows us to do is change memory dividers to either increase or decrease memory speed while keeping the CPU bus the same. We then tried DDR2-889 5-5-5-15, but this failed test 5 with a massive number of errors.
533MHz
667MHz
750MHz
800MHz
840MHz
870MHz
885MHz
900MHz
Crucial Ballistix PC2-6400 2GB
4-3-3-12 2.0v
4-3-3-12 2.1v
4-3-3-12 2.2v
4-4-4-12 2.2v
4-4-4-12 2.2v
4-4-4-12 2.3v
4-4-4-12 2.35v
FAIL
Corsair Value Select PC2-5300 2GB
4-4-4-12 2.0v
4-4-4-12 2.0v
FAIL
FAIL
FAIL
FAIL
FAIL
FAIL
Knowing that the processor can manage at least 4.2GHz with full stability, we opted to keep the memory set for DDR2-800 operation at the 266MHz bus, and slowly increase FSB until we hit the limit of the memory. The first wall came at DDR2-855 (285MHz FSB) where we had to raise memory voltage from 2.2v to 2.3v. This allowed us to run right on till DDR2-885 before having to increase voltage again, to 2.35v. At this setting, we could run DDR2-885 100% stable at 4-4-4-12 timings, however the next jump to DDR2-900 (300MHz FSB) wasn’t quite stable even with 2.4v. 2.4v is the maximum vdimm on the P5WD2-E motherboard. Still, DDR2-885 at 4-4-4-12 timings offers simply incredible performance; we noted the 4606MB/s unbuffered memory benchmark in Memtest itself!
However it wasn’t all fun and games, as we experienced some issues running DDR2-800 when the front side bus was at 300MHz. However hard we tried, we could not get Memtest to run 100% stable through test 5, although other tests would complete with no errors. Since we know the memory can definitely do DDR2-800, and the motherboard can definitely do DDR2-800 at 200 and 266MHz FSB, we must attribute this behaviour to a bug with that particular memory divider at high bus speeds. The best performance from the system was actually had at DDR2-750 4-3-3-12 with a 300MHz FSB, and with the vdimm at the rated 2.2v. This shows the Crucial Ballistix is an excellent jack of all trades!
In contrast to the Crucial, the Corsair PC2-5300 would refuse to run at any speed higher than DDR2-720, and even then ‘only’ at 4-4-4-12 timings. We tried DDR2-800 with the Corsair, but were met with a no POST situation. We’ll be taking a look at the effects of DDR2 speed and latency on system performance in a future DDR2 memory module roundup.
