After a month and a half using AHCI, I went back to IDE. Some of you might be interested in the reasons: 1. Burst rate is significantly worse with AHCI. HDTune reports 120MB/s with AHCI versus 140MB/s with IDE HD Tach reports 200MB/s with AHCI versus 225MB/s with IDE. (why Tune & Tach don't give the same values is a mystery, but in all cases IDE > AHCI) 2. CPU consumption is definitely higher when using AHCI compared to IDE for seemingly no speed increase whatsoever. 3. AHCI introduces a HDD sleep bug ! I have 2 HDDs. In XP (SP3) power management, I set to switch off the HDDs after 2 hours of inactivity. When I'm using AHCI, the 2nd HDD never goes to sleep, EVER, if the first one isn't already asleep. With the same power management settings under IDE, no problem, 2nd HDD goes to sleep after desired time alright even if first HDD keeps being active. 4. Resume from standby is a bit slower. So for now i'll forget about AHCI for my current config. Btw, going back to IDE is easy as hell, just swith back to IDE in BIOS, reboot and all is fine. If you're sure you won't be ever going back to AHCI you can remove the intel matrix storage manager driver (iaStor) Later, TSR