Beware Prefetch Settings

**kpjuk** · 01-28-2005, 04:29 PM

In an effort to get close to some of the boot times attained by some of the guys in this forum, I have been playing with nLite, XPLite and XPultralite

A performance tip I came across was to change the EnablePrefetcher value in
[HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control \ Session Manager \ Memory Management \ PrefetchParameters] to a value between 5 and 9.

This gave me a significant performance change, from 17 secs to 28 secs !

A principle when tweaking to bear in mind is change 1 thing only at a time. I have been through the values from 1 to 5, and the default value of 2 followed cloesly by 3 gave me the best performance overall. A lot of these tweaks depend on what kit you have and what else you have installed and running.

Tweakers beware !

KPJUK

**egeekial** · 01-28-2005, 04:32 PM

Do you have any idea what exactly this does?

EDIT: Found it. http://www.iamnotageek.com/a/94-p1.php

**kpjuk** · 01-28-2005, 04:57 PM

My point is that not every performance tip you come across is a performance tip.

http://arstechnica.com/guides/tweaks/sgp-tweaks.ars

**momanz** · 01-28-2005, 09:16 PM

I've played around with the prefetcher settings quite a bit, here are what the settings do...

1 = Boot prefetch
2 = App Prefetch
3 = Both

Anything higher I believe disables the prefetcher. Look in your windows folder and you'll find a folder labeled prefetch. Within that folder you will see several files that contain information about a) specific applications that are launched b) a file named NTOSBOOT-B00DFAAD.pf and c)a file layout.ini

The OS uses the information in these files to speed up the boot process (NTOSBOOT-B00DFAAD.pf) and the time it takes to launch of your applications. The settings above control which files get written. If you select 1 only the NTOSBOOT-B00DFAAD.pf is written and used. If you select 2 only the application prefetch files are written.

Bottom line, leave things set to 3 for best performance unless you have a good reason (like you are using EWF) not to. Another subtlety of the prefetcher that you should be aware of is that any changes to your startup driver or service configuraton will initially increase your boot time, the OS is expecting a startup sequence that is described by the in the prefetch file. The new configuration means a little extra work for the OS (more time to boot). After new prefetch data has been written 3-5 times to the boot prefetch file things seem to return to the fastest boot.