I use "WD10EARS", or more descriptive: Western Digital, SATA 2, 1TB, 7200rpm, 64MB cache. I have no idea what's the problem, but the average speed of the disk is 5 MBps and it's awful. I tried defragmenting, some WD disk checker, disabling win write-cache buffer flushing... etc. but nothing helped.
Motherboard: ASUS P5KPL-AM SE
A month ago I was using WD, SATA, 320GB, 7200rpm, 8MB cache and it was 5 to 6 times faster than this one.