为什么高IO速率操作会减慢linux上的所有操作?

This may be slightly OT, but I was wondering why having a process which heavily uses IO (say cp big file from one location to the other on the same disk) slows everything down, even processes which are mostly CPU bound. I noticed that on both OS I heavily use (mac os x and linux).This may be slightly OT, but I was wondering wh