PREFETCH What Really do it do ?

[Mike Baudoux]

Cleaning the Prefetch Directory
Added 3/2/03

WindowsXP has a new feature called Prefetch. This keeps a shortcut to
recently used programs.
However it can fill up with old and obsolete programs.

To clean this periodically go to:

1.. Star / Run / Prefetch
2.. Press Ctrl-A to highlight all the shortcuts
3.. Delete them

What do it really do is it A Required tool too use ?


Thanks

Mike

 

[Crusty \(-: Old B@stard :-\)]

It is self cleaning and you really don't have to do anything!

--
Regards:

Richard Urban

aka Crusty (-: Old B@stard

 

[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).

 

[Kelly]

Hi Mike,

The Prefetcher component in Windows XP is part of the Memory Manager, and
helps to shorten the amount of time it takes to start Windows and programs.

Windows XP "monitors" itself and notices which applications are launched
frequently. It gathers information about these applications and what they
access with the launch and stores this information in the prefetch folder.

It then uses this information to "optimize" access to these files so that
they launch faster.

Once every three days, by default, Windows XP will perform a partial
defragmentation and adjust the layout of the disk based upon current use.
The files to be moved are written in the file Layout.ini (found in the
Prefetch directory under the System Root directory).

More information here on the Prefetch Folder in Windows XP
http://www.kellys-korner-xp.com/xp_p.htm#xp_prefetch

 

[Alex Nichol]

Cleaning the Prefetch Directory
Added 3/2/03

WindowsXP has a new feature called Prefetch. This keeps a shortcut to
recently used programs.
However it can fill up with old and obsolete programs.

To clean this periodically go to:

1.. Star / Run / Prefetch
2.. Press Ctrl-A to highlight all the shortcuts
3.. Delete them

That is not good advice.

When a program is loaded, a record is put, or updated, in the
corresponding file in Prefetch, detailing what files it uses, in what
order. Boot of the system has such a record, too

From that two things happen.

One - when a load is started in future, the system arranges to get the
expected files into RAM straight away, without waiting to be asked, and

Two - every three days, a sort of semi-defrag run is done in a quiet
period, which arranges files so that such sets will be able to load as a
smooth stream without need to hunt around the disk for them. The boot
side of this speeds load of the system: the Bootvis program does a
preliminary optimisation of their layout, but it will take place, and
better, through the automatic process. The details of the best layout
are kept in the layout,inf file which is checked and updated each time
this optimisation runs, for the best overall performance. This can be
used for optimisation alternatively by some third party defrag programs,
eg Perfect Disk Pro

Two points:

Contrary to what is said, it is *not* necessary to empty prefetch. Any
program that does not get used for a week or so will have its file
dropped out anyway: ones that are rarely used get low priority in
optimisation

and:
The optimisation at regular intervals is initiated by task scheduler so
you need to have it running for this to work (also for System Restore
to make its daily restore point) even though no scheduled task appears
if you look in control Panel - Scheduled tasks. Check the Advanced menu
there, and if it says 'Start Using. . ' click that so it says 'Stop
using . . .' It then looks for a time when the system is quiescent (I
think it waits for 15 mins of no disk activity, but am not sure on
that). This is one reason for the query 'my hard disk goes chattering
when I am doing nothing'; the other being search engine indexing.

 

[PA Bear]

Nicely done, Alex, as always.
--
~Robear

That is not good advice.

When a program is loaded, a record is put, or updated, in the
corresponding file in Prefetch, detailing what files it uses, in what
order. Boot of the system has such a record, too

From that two things happen.

One - when a load is started in future, the system arranges to get the
expected files into RAM straight away, without waiting to be asked, and

Two - every three days, a sort of semi-defrag run is done in a quiet
period, which arranges files so that such sets will be able to load as a
smooth stream without need to hunt around the disk for them. The boot
side of this speeds load of the system: the Bootvis program does a
preliminary optimisation of their layout, but it will take place, and
better, through the automatic process. The details of the best layout
are kept in the layout,inf file which is checked and updated each time
this optimisation runs, for the best overall performance. This can be
used for optimisation alternatively by some third party defrag programs,
eg Perfect Disk Pro

Two points:

Contrary to what is said, it is *not* necessary to empty prefetch. Any
program that does not get used for a week or so will have its file
dropped out anyway: ones that are rarely used get low priority in
optimisation

and:
The optimisation at regular intervals is initiated by task scheduler so
you need to have it running for this to work (also for System Restore
to make its daily restore point) even though no scheduled task appears
if you look in control Panel - Scheduled tasks. Check the Advanced menu
there, and if it says 'Start Using. . ' click that so it says 'Stop
using . . .' It then looks for a time when the system is quiescent (I
think it waits for 15 mins of no disk activity, but am not sure on
that). This is one reason for the query 'my hard disk goes chattering
when I am doing nothing'; the other being search engine indexing.

 

[Jim Carlock]

Question... Does it show up as an event in the Task Scheduler?
Is it logged somewhere?

I can see that the Prefetch is getting used, by looking at the date
and time stamps on the files, but there are no events logged in
Scheduler, Advanced, View Log. All I see in the events log there
is Scheduler started with no mention of what was started.

"Task Scheduler Service"
Exited at 6/9/2004 12:14:20 AM
"Task Scheduler Service"
Started at 6/9/2004 12:15:27 AM
[ ***** Most recent entry is above this line ***** ]

Thanks Alex, PA Bear.

--
Jim Carlock
http://www.microcosmotalk.com/
Post replies to the newsgroup.


:
Nicely done, Alex, as always.

 

[Alex Nichol]

Question... Does it show up as an event in the Task Scheduler?

No it doesn't

Is it logged somewhere?

Not that I know of - but I have not looked very hard, and for myself use
the Perfect Disk Defragger, taking over the use of the recorded info
rather than letting the normal 3 day affair do the rearrangement.