In all Windows versions up to XP and Win2K3 server is known that the process priority settings have very little effect. So unless the process is really stuck in a tight loop, there’s almost no difference if the priority is say Normal or High.
This is mostly caused by the fact that priorities only influence the thread scheduler - and not I/O.
Under Windows Vista, this should have changed. There is the concept of “low priority I/O”, i.e. if a process (or thread) runs with a low priority level, the I/O requests it initiates will also have lower priority.
Is this really true, i.e., is the system able to distinguish between what needs to be done fast (such as paging) and what can wait (such as background antivirus scanning)? ???