Odd HD performace drop spikes in HDTach when running under XP Pro x64 ?

[Defenestration]

I am/was considering running XP Pro x64 as my main OS on my new PC, but was a bit dismayed when I installed XP Pro x64 SP2 and ran HDTach. While the average read performance was comparable to when running under XP Pro 32-bit (approx. 71MB/s with my superb Western Digital WD5000AAKS), I noticed that there were about 3 or 4 dropout troughs during the benchmark when running under x64.

Does anyone know why this might be ?

PS. When I have my new machine back up and running, I will post the HDTach results for the same WD5000AAKS drive when running under XP 32-bit and XP x64 so you can see what I mean.

[arthurleung]

If your windows happens to read/write from the drive when you're running HDTach, it will produce the troughs. It is fine as HDTach and any other speed test are just benchmarks not real-life performance. You'll never feel the "bump". If you do, I strongly suggest you switch to a Raptor 150G

Also if you do a few more tests you'll probably see them happening in different parts of the disk.

[Defenestration]

But why do these drops happen on XP x64, but not on XP 32-bit ?