That and certain drives also have a mind of their own and ignore any hdparm APM setting after a short while in favour of their own, absurdly aggressive setting. One I have (by default) unloads after 8 seconds of inactivity and the only way to change it is by some obscure DOS utility that I can't get to work. 8 seconds is crazy-low, and because the typical interval for disc activity on a Linux system under enthusiastic use is typically 10-15 seconds (or even when a bit idle, as lots of other things touch the filesystem in the backgrounds), the heads spend a lot of time loading and unloading. It's possible to tune the Linux VM subsystem to ouch the disc less often, but in practise doesn't make much of a difference. Windows XP does exactly the same. The disc manufacturer says Linux should not wake up the disc so frequently, but I don't see how that squares with the way a modern, multitasking operating system works; things touch the filesystem, and this must be synced in good time (I don't want 30 seconds' worth of dirty data just sitting in RAM). And besides, disc manufacturers should just make discs and leave VM policy to kernel designers.