what exactly is prefetch ?

[DAN COLODNEY]

i've read several posts and replies here concerning "prefetch" and realize
that i don't know what the heck "prefetch" is and what it does.

if i type "prefetch" in the RUN command i get numerous files such as
RUNDLL32.EXE-4FF9832D.pf, LOGONUI.EXE-312BE1BF.pf. are these important?
should i delete them? what's the downside and upside to having them or not
having them? thanks, dan

 

[Rick \Nutcase\ Rogers]

Hi,

Prefetch is part of the memory manager and should be left alone outside of
test and troubleshooting environments. It helps the system load frequently
used files faster.

--
Best of Luck,

Rick Rogers aka "Nutcase" MS-MVP - Win9x
Windows isn't rocket science! That's my other hobby!

Associate Expert - WinXP - Expert Zone

 

[Carey Frisch [MVP]]

The Prefetch folder contains information regarding the optimal disk layout
of program files so they launch quicker. You may delete all those files,
but XP will rebuild that folder so that your computer runs as efficiently
as possible. After deleting the prefetch files, your computer's performance
will suffer slightly until the prefetch folder is rebuilt. It takes approximately
three computer reboots to properly rebuild the prefetch folder contents.

Windows XP's Built-In Optimization
http://www.extremetech.com/article2/0,3973,1149277,00.asp


--
Carey Frisch
Microsoft MVP
Windows XP - Shell/User

------------------------------------------------------------------------------------------------
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| i've read several posts and replies here concerning "prefetch" and realize
| that i don't know what the heck "prefetch" is and what it does.
|
| if i type "prefetch" in the RUN command i get numerous files such as
| RUNDLL32.EXE-4FF9832D.pf, LOGONUI.EXE-312BE1BF.pf. are these important?
| should i delete them? what's the downside and upside to having them or not
| having them? thanks, dan

 

[R. McCarty]

Prefetch essentially is a Boot/Application start time enhancer.
The process monitors both the Boot sequence and every application
start. It creates a .PF (Prefetch File) that contains data on what code
is loaded and where on the disk the code is found. At a fixed interval
these .pf files are collated into a module called Layout.Ini. Defrag then
takes Layout.Ini and defrags, placing the code in contiguous areas of
the disk drive. In layman's terms it essentially packs all the key code
modules into a disk area where it can be loaded very quickly. As far
as Boot time goes the benefit comes from "Parallel" loading. In earlier
versions of Windows it would load one driver or service then the next.
In XP, because of the layout, multiple drivers/services & apps can be
started simultaneously. This can viewed by using BootVis to see what
activities happen during boot and the sequence and time duration of
each.
Windows constantly monitors and updates the files inside of the folder
C:\Windows\Prefetch. If you count the .PF files in prefetch and recheck
perhaps a week later you will notice a change in the count. Many sites
recommend purging out the Prefetch folder. It doesn't harm anything,
but Windows will have to recreate and start over with the monitoring
and placement process.
Prefetch has four operational modes in a Dword Registry Key
"Enable Prefetcher"
0 = Disabled
1 = Boot Prefetch Only
2 = Application Prefetch Only
3 = Both Boot and Application Prefetch (Default).

 

[JAX]

Your explanation of prefetch is the most complete I've seen yet. I've
somehow disabled my prefetch and am looking for help. Where in the registry
is prefetch located? If I can find it, I probably can solve my problem,
thanks to your information in this post.

TIA JAX

 

[DAN COLODNEY]

thanks very much. great explanation.
dan

Prefetch essentially is a Boot/Application start time enhancer.
The process monitors both the Boot sequence and every application
start. It creates a .PF (Prefetch File) that contains data on what code
is loaded and where on the disk the code is found. At a fixed interval
these .pf files are collated into a module called Layout.Ini. Defrag then
takes Layout.Ini and defrags, placing the code in contiguous areas of
the disk drive. In layman's terms it essentially packs all the key code
modules into a disk area where it can be loaded very quickly. As far
as Boot time goes the benefit comes from "Parallel" loading. In earlier
versions of Windows it would load one driver or service then the next.
In XP, because of the layout, multiple drivers/services & apps can be
started simultaneously. This can viewed by using BootVis to see what
activities happen during boot and the sequence and time duration of
each.
Windows constantly monitors and updates the files inside of the folder
C:\Windows\Prefetch. If you count the .PF files in prefetch and recheck
perhaps a week later you will notice a change in the count. Many sites
recommend purging out the Prefetch folder. It doesn't harm anything,
but Windows will have to recreate and start over with the monitoring
and placement process.
Prefetch has four operational modes in a Dword Registry Key
"Enable Prefetcher"
0 = Disabled
1 = Boot Prefetch Only
2 = Application Prefetch Only
3 = Both Boot and Application Prefetch (Default).

 

[Rick \Nutcase\ Rogers]

Hi,

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory
Management\PrefetchParameters

Locate the Enableprefetcher value and change it from 0 to 3.

--
Best of Luck,

Rick Rogers aka "Nutcase" MS-MVP - Win9x
Windows isn't rocket science! That's my other hobby!

Associate Expert - WinXP - Expert Zone

 

[JAX]

Thank you Rick,

The problem was, I had disabled Task Scheduler in services. I reset it to
automatic and, all is well. It is good to know where the key is though.

Cheers, JAX