EnablePrefetcher in PrefetchParameters

I remember that several tweaking programs that emerged after the release of Windows XP changed the EnablePrefetcher in the Registry which supposedly should speed up application load time. I also read about that tip in many forums and just recently in a computer magazine that published the tip to change the EnablePrefetcher value to 4-6 to speed up the system.

I was astonished to read this tip in a well respected magazine and would like to use this article to clarify it. You can find the current EnablePrefetcher value in your Registry. Navigate to the key HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control \ Session Manager \ Memory Management \ PrefetchParameters. The default value for the string should be 3 which means that prefetching is enabled for application launch and boot.

Other values are 0 for disabling prefetching, 1 to enable it for application launch only and 2 to enable it for boot only. The optimal setting is the default one which is 3. Setting EnablePrefetcher to a value above 3 has no effect at all. Even systems with low RAM should keep the default setting of 3 because they actually do benefit from prefetching.

My suggestion would be to check the Registry key on your system to make sure that the value is set to 3. If it is not change it to 3 and you will probably witness great speed improvements.

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Tags: EnablePrefetcher, prefetcher, registry, windows tips
Categories: Knowledge, Operating Systems, Windows

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One Response to “EnablePrefetcher in PrefetchParameters”

1. Larry Miller says:

   December 3, 2008 at 8:45 pm

   Good article.
   One observation – values above 3 will be equivelant to valid values. The registry entry is used to independently control both boot and application prefetching. The result is obtained by ANDING bits 0 and 1, for a maximum value of 3. Setting a value over 3 will set bits 2 or 3 which are undefined. Microsoft has always warned that this paractice is dangerous.

   The equivelant values are as follows:
   4 = 0
   5 = 1
   6 = 2
   7 = 3
   8 = 0
   9 = 1

   It should also be added that “cleaning” or deleting the contents of the prefetch folder will impair performance. It is based on a complete msunderstanding of how prefetch works.

   Proper prefetch operation requires that the Task Scheduler service be enabled and set to Automatic. Otherwise prefetch will be crippled, leading to impaired performance.

   Larry Miller
   Microsoft MCSA

   Reply