Disk positioning system


Move head to specific track and keep it there
Resist physical socks, imperfect tracks, etc.
A seek consists of up to four phases
speedup--accelerate arm to max speed or half way point
coast--at max speed (for long seeks)
slowdown--stops arm near destination
settle--adjusts head to actual desired track
Very short seeks dominated by settle time (~1 ms)
Short (200-400 cyl.) seeks dominated by speedup
Accelerations of ~40g