What Prefetching does...
[[Windows XP Professional monitors the files that are used when the computer
starts and when you start applications. By monitoring these files, Windows
XP Professional can prefetch them. Prefetching data is the process whereby
data that is expected to be requested is read ahead into the cache.
Prefetching boot files and applications decreases the time needed to start
Windows XP Professional and start applications.

Prefetching is further improved if the files are located next to each other
on the outer edge of the disk. Windows XP Professional optimizes the
location of boot files and applications when the computer is idle. The
optimization occurs in the background and lasts only a minute or two; you
might hear the hard disk being accessed when optimization occurs. After the
initial optimization takes place, subsequent optimization occurs, at most,
every three days.

When you run the Disk Defragmenter tools that are included with Windows XP
Professional, they can perform any optimization updates that are scheduled
to take place during the next idle period. The Disk Defragmenter tools do
not disturb the existing layout of optimized boot files and applications.

Note
Computers running Windows XP Home Edition also prefetch and optimize boot
files and applications.]]
Optimizing Startup Times by Using Defragmentation Tools
http://www.microsoft.com/resources/d...d_tro_uutk.asp

ProcessIdleTasks
Idle Task Scheduling: The ProcessIdleTask API
http://www.microsoft.com/whdc/system...mark.mspx#EDAA

Disable Prefetching then.

UNChecking TweakUI's Optimize hard disk when idle will disable prefetcher.

Optimize hard disk when idle
This allows Windows to rearrange files on the hard disk when the computer is
not in use to improve performance. This is a system wide setting which
requires a restart for changes to take effect.

Change Enable to N
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Dfrg\BootOpt imizeFunction

Enable
[[Accepted values for this entry are Y or N. If the entry is set to Y,
Windows automatically optimizes the file location for boot optimization.
This optimization occurs automatically if the system is idle for 10 minutes.
Boot optimization improves startup time by locating startup files in
contiguous clusters on the volume, reducing the movement of the disk head
when reading the volume.]]

Change EnablePrefetcher to 0.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\
Session Manager\MemoryManagement\PrefetchParameters

EnablePrefetcher values are:
0 = disabled
1 = Application launch prefetching
2 = Boot prefetching
3 = Both Application & boot prefetching

Also, if these services are disabled, Prefetcher will not work:
System Event Notification
Task Scheduler

--
Hope this helps. Let us know.

Wes
MS-MVP Windows Shell/User

In news:6C0C5725-463D-46FF-9CC6-40C9BA8503D3@microsoft.com,
mbs6 <mbs6@discussions.microsoft.com> hunted and pecked:
> I have a machine running Win XP Home and whenever the machine is idle for
> a while the system disk goes nuts with reads and writes and never stops.
> I finally determined that defrag.exe and dfrgntfs.exe are the processes
> responsible. Somehow they are starting up whenever the machine is idle.
> It is driving me crazy as it never completes and causes my disk drive to
> always be in use. I suppose somewhere in the bowels of windows it has
> decided to take idle moments to optimize data on the disk. I DON'T WANT
> IT TO DO THIS WITHOUT ME ASKING IT TO!
>
> Somebody, somewhere at Microsoft knows why/how this is happening. Please
> clue in the rest of us.