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XP File prefetch

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12 replies to this topic

#1
vinifera

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can someone explain me how can prefetch actualy speed up things
if lets say user disables task scheduler (crappy service anyway) and doesnt defragment
hard drive/partiton effectively

i mean, MFT already contains position of files, and prefetch has the same but only with most used files
so disk actualy has to SEEK-->MFT--->SEEK FOR PREFETCH LIST-->SEEK FILES
and if disk/partiton is fragmented this would slow it down

i always defrag my system partiton to have EXE and DLL files on outer tracks of HD so seeking is smallest
and MFT is close to outer tracks too, without prefetch this is fast, but with prefetch its double the seek/acces

or is my logic wrong ?

Edited by vinifera, 17 October 2009 - 08:04 PM.

If you want true Windows user experience
try Longhorn builds: 3718, 4029, 4066


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#2
DreamSkape

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Hi Vinifera,

Your logic is not wrong at all. The prefetch is just a one of the many gimmicks that MS shows off to make it seem the best thing. You must how noticed the accelerators in IE8 (http://bit.ly/5QtpG). How many of us use them? And are they really accelerators? For example, the email accelerator just takes you to your email provider - but still ppl think that IE8 is gr8. Your email client is more faster than those accelerators.

Same logic with prefetch: Showing off something that is not really useful. Logically thinking, it is an added process to further slow down the functioning of machines with lower memory.

Another similar process is the Settings Transfer Wizard. It never worked for me. Neither did the Windows default Backup in System Tools.

Software Biz also needs to show off as with anything. Anything claiming to offer more - sells more.

Microsoft is not the same as it used to be. With Allen cornered and Gates surrounded with stupid advisors, they are ruining a hard built company (The complete story of MS minus its negatives: http://bit.ly/rmj47). I was surprised to see that IE is not their own product nor was Basic. They did work on Basic but IE, they literally stole it from a third party vendor.


Guess, m going off-topic.

Keep me posted... would like to hear more on MS issues that are growing day by day.

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Signed: Sunday, October 18, 2009, 11:35:27 AM IST

#3
engmod

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>i always defrag my system partiton to have EXE and DLL files on outer tracks of HD so seeking is smallest
and MFT is close to outer tracks too, without prefetch this is fast, but with prefetch its double the seek/acces

Cylinder zero is closest to the centre of the disk, so I think you want to put your dll's on the inside.

VMS whose file system was used as a start for NTFS always had the MFT in the centre of the disk to reduce seeking.
Then you cluster your exe's and dll's close to the centre.

Derek

#4
Ponch

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Cylinder zero is closest to the centre of the disk, so I think you want to put your dll's on the inside.

Can you please explain how the center of the disk would be faster at seeking/reading ?

#5
vinifera

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he can't :)

and NO, anything from center and lowers makes slower seeking
because your space is getting smaller and your files start to take more tracks
so HD needle actualy has to seek more up and down
while on the edge of disk you have plenty of lets call it wide space
so less tracks are being used at "longer" space, so seeking is minimum

as for MFT, no it is not centered, MFT reserves its space accordingly to system change
sometimes its smaller and sometimes its bigger, its default setting is to be close
to PageFile and be placed close to the edge
If you want true Windows user experience
try Longhorn builds: 3718, 4029, 4066

#6
Phenomic

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I too think that prefetch is an anachronism and not necessary with modern hard disks. How does one turn it off?

#7
vinifera

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in XP you have to turn it off via registry (google it)
in vista/7 there is service under services.msc to disable it
If you want true Windows user experience
try Longhorn builds: 3718, 4029, 4066

#8
fdv

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I deny permission to the system at install time.

I expanded DEFLTWK.IN_

I commented out:

"%SystemRoot%\Prefetch",1,"D:AR"

I added:

"%SystemRoot%\Prefetch",2,"D:PAR(D;;FAGAGRGWGXWD;;;SY)"

I makecab'ed the file and renamed the original to .OLD

Now when I install, the directory doesn't get created

Ha!

#9
engmod

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>Can you please explain how the center of the disk would be faster at seeking/reading ?

perhaps I should have said closest to the spindle.

That is where the heads first 'land'

#10
engmod

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he can't :)

and NO, anything from center and lowers makes slower seeking
because your space is getting smaller and your files start to take more tracks
so HD needle actualy has to seek more up and down
while on the edge of disk you have plenty of lets call it wide space
so less tracks are being used at "longer" space, so seeking is minimum

as for MFT, no it is not centered, MFT reserves its space accordingly to system change
sometimes its smaller and sometimes its bigger, its default setting is to be close
to PageFile and be placed close to the edge


I disagree and so does the architect who designed VMS.
If the MFT is at the centre cylinder and files around it (read both sides) then the disk throughput will be quicker than if the MFT is at one end of the disk.

Moot point however with SSD's taking over the world.

Edited by engmod, 31 October 2009 - 08:47 PM.


#11
vinifera

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true, my comment was more directed toward Prefetch and .exe and .dll files which "settings"
are stored in Prefetch and most used by user/system

Edited by vinifera, 18 November 2009 - 09:12 PM.

If you want true Windows user experience
try Longhorn builds: 3718, 4029, 4066

#12
JRosenfeld

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Prefetch loads the most often used files into any available RAM so that when they are needed it is quicker than having to load them from disk.

Edited by JRosenfeld, 21 November 2009 - 09:30 AM.


#13
Mr Snrub

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Prefetch loads the most often used files into any available RAM so that when they are needed it is quicker than having to load them from disk.

Mixing up XP's prefetch and Vista's system cache usage there.

Prefetch waits for a process to start and then monitors the file I/O activity for the first portion of its lifetime, making a note of the files requested and in which order.
On subsequent launches, the prefetch (.pf) file for that specific process is used to read the files in before the application has actually requested them - so when the application gets round to sending the file open request it incurs no disk I/O.

Prefetch is only effective when the process requests the same files each time, otherwise the prefetcher loads in files that don't get used.
It only makes an attempt to reactively pre-load files on a per-process basis when the process fires up.

(Vista's Superfetch is a lot smarter and prefetches files before the application is even launched, if the user's activity is consistent.)

The system cache on XP is a limited resource, regardless of the RAM, and it isn't prepopulated because there is no Superfetch.
On Vista, the system cache can use almost all physical memory (as "free RAM is wasted RAM").

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