Use of prefetch folder in XP
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fun2sh
Pawned!... Beyond GODLIKE
Myth - "Adding the /Prefetch:1 Switch to the startup path of a program's shortcut will decrease the program's startup time."
Reality - All it does is change your hash number - the OS is doing exactly the same thing it did before, and just saving the prefetch pages to a different file. It does not improve performance in any way. Ryan Myers of Microsoft's Windows Client Performance Team writes: "The /prefetch:# flag is looked at by the OS when we create the process - however, it has one (and only one) purpose. We add the passed number to the hash. Why? WMP is a multipurpose application and may do many different things. The DLLs and code that it touches will be very different when playing a WMV than when playing a DVD, or when ripping a CD, or when listening to a Shoutcast stream, or any of the other things that WMP can do. If we only had one hash for WMP, then the prefetch would only be correct for one such use having incorrect prefetch data would not be a fatal error - it'd just load pages into memory that'd never get used, and then get swapped back out to disk as soon as possible. Still, it's counterproductive. By specifying a /prefetch:# flag with a different number for each "mode" that WMP can do, each mode gets its own separate hash file, and thus we properly prefetch. (This behavior isn't specific to WMP - it does the same for any app.) This flag is looked at when we create the first thread in the process, but it is not removed by CreateProcess from the command line, so any app that chokes on unrecognized command line parameters will not work with it. This is why so many people notice that Kazaa and other apps crash or otherwise refuse to start when it's added. Of course, WMP knows that it may be there, and just silently ignores its existence. I suspect that the "add /prefetch:1 to make rocket go now" urban legend will never die, though." - Source - Source 2
Cleaning the Prefetch Folder
Myth - "Deleting the contents of the Prefetch folder improves performance."
Reality - "Every time you delete an application's Prefetch (.PF) file you will cripple that application's load time the next time you go to launch it. This can temporarily increase load times by as much as 100%. For one thing, XP will just re-create the Prefetch (.PF) trace files anyway; secondly, it trims the files if there's ever more than 128 of them so that it doesn't needlessly consume space. However you do not regain optimal application load times back until after the second time you launch the same application due to the Prefetch (.PF) trace file being re-created. Prefetch (.PF) trace files are not a cache and are not preloaded into memory upon windows startup. They are never even accessed until you launch an application. Only one Prefetch (.PF) trace file per application is created. There is never ANY reason to delete these files. Cleaning the Prefetch folder is actually a temporary self-inflicted unoptimization. Why you would want to deliberately hurt your PC's performance I have no idea." - Source - Source 2 - Source 3 - Source 4 - Source 5
Malware/Viruses - Some people irresponsibly recommend cleaning this folder due to possible Malware/Virus infection. Malware/Viruses can place an infected file(s) in any folder and the Prefetch folder is no different. Do these same people recommend deleting the contents of the Windows folder because it is a popular location to find an infected file(s)? Of course not, you simply clean or delete the infected file(s) not the contents of the folder. This Myth got started due to the indiscriminate nature of the Windows Prefetcher, which will Prefetch any executable file that you load or loads during Windows start up. Thus it is quite common on an infected machine to find a Prefetch (.PF) trace file in the Prefetch folder with the same name as an infected executable. These files are NOT Malware/Viruses. They are there to improve the load time, in this case ironically, of the Malware/Virus but do not contain any infected code. Once the associated infected executable is deleted, these Prefetch (.PF) trace files do nothing and will eventually automatically be cleaned by Windows.
Corrupted Files - Some people claim that Prefetch (.PF) trace files can get randomly "corrupted" and thus they need to be periodically deleted. Files do not get "corrupted" unless something is wrong with your computer. Any file corruption is a warning sign something is wrong with your system. Overclocking, using defective components like Memory and Harddrives and using FAT32 instead of the superior NTFS file system are common causes of file corruption. NTFS is very resilient to file corruption as compared to FAT32. When storing data to disk, NTFS records file I/O events to a special transaction log. If the system crashes or encounters an interruption, NTFS can use this log to restore the volume and prevent corruption from an abnormal program termination or system shutdown. NTFS doesn't commit an action to disk until it verifies the successful completion of the action. This precaution helps prevent corruption of an NTFS volume. NTFS also supports hot-fixing disk sectors, where the OS automatically blocks out bad disk sectors and relocates data from these sectors. This housecleaning happens in the background. An application attempting to read or write data on a hot-fixed area will never know the disk had a problem. Thus the solution is fixing the cause of the file corruption.
CCleaner - Finally the useless, performance slowing cleaning option "Old Prefetch data" was moved to the advanced section and is now not selected by default. Never select this option for cleaning as it will increase application and Windows load times. This option removes Prefetch files that are a few weeks old based on the NTFS last access date. Since Windows XP already cleans this folder at 128 entries, this is a useless option that will only reduce system performance. You should never delete a Prefetch file for any installed application since that would cripple it's load times. Just because a program was not used in a few weeks does not mean you want it to load as slow as possible when you do decide to use it. If you disable the NTFS last access date stamp then this option will delete the whole contents of the Prefetch folder after a few weeks, which will cripple Windows Boot and all application load times. The Prefetch folder is also ridiculously small so cleaning Prefetch files before the 128 limit will reclaim next to no disk space. This option clearly needs a warning to prevent people from unknowingly hurting their system performance. Anyone who claims this should be cleaned for ANY reason does not understand how Windows Prefetching works. - Source
Bad Advice - This bad advice to clean the prefetch folder is posted frequently on the Internet by people who do not understand how the Windows XP Prefetcher works. Their explanations are 100% inaccurate. - Bad Advice 1 - Bad Advice 2 - Bad Advice 3 - Bad Advice 4
EnablePrefetcher
[HKLM\SYSTEM\CurrentControlSet\Control\SessionManager\MemoryManagement\PrefetchParameters] "EnablePrefetcher"
Myth - "Setting any value higher then 3 to EnablePrefetcher will improve performance."
Reality - 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. This is a new feature in Windows XP which improves application load times and Windows boot times automatically. The slower your system and the larger an application, the more Prefetching helps. Even high end systems benefit from prefetching with large, slow loading applications, such as large games. By default Prefetching is enabled in Windows XP and already configured optimally. The following list describes the different possible values for the EnablePrefetcher registry key.
0 = Disabled
1 = Application launch prefetching enabled
2 = Boot prefetching enabled
3 = Applaunch and Boot enabled (Optimal and Default)
By default the Prefetcher is set to a value of 3 in Windows XP. Values such as 4, 5, 6 ect... do not exist and are thus useless. Leave this at the default value of 3 which is already optimal for maximum performance on both Windows XP Boot and initial application launches. - Source
Low Memory Systems - Recommendations to disable Prefetching on low memory systems (128 MB - 512 MB) is based on the fallacy that portions of application code are preloaded into memory before the application load is initiated during Windows startup. This is completely false and is spread by people who do not understand how Windows XP Prefetching works. The slower the system the more it will benefit from Prefetching. 64 MB systems will suffer due to insufficient RAM, reducing but not eliminating Window XP's prefetching benefits. 128 MB is the recommended minimum for optimal prefetching performance.
Boot Performance - Recommendations to set the EnablePrefetcher value to 2 to improve boot performance is based on the fallacy that portions of application code are preloaded into memory before the application load is initiated during Windows XP startup. This is completely false and is spread by people who do not understand how Windows XP Prefetching works. Only the files used during boot will be Prefetched. The Prefetch folder is not a cache. Windows XP will boot in the exact same amount of time with either value 2 or 3, the only difference with 2 is that now all of your initial application launches will not be Prefetched and thus load slower. The default value of 3 in no way negatively affects Windows XP boot times. Leave the value at 3 for optimal Windows XP boot and initial application launch times.
Enable Superfetch
[HKLM\SYSTEM\CurrentControlSet\Control\SessionManager\MemoryManagement\PrefetchParameters] "EnableSuperfetch"
Myth - "Adding EnableSuperfetch to the registry improves performance in Windows XP as it does in Windows Vista."
Reality - "This myth was started when the Inquirer irresponsibly ran a bogus letter without doing any fact checking. Windows internals guru Mark Russinovich said this won't work, the "Superfetch" string isn't even in the Windows XP kernel. You can confirm this yourself by checking with the strings.exe utility. This makes it impossible for it to do anything since no "Superfetch" command exists. Windows cannot execute a nonexistent command and will simply ignore it. Anyone who says this works is not only lying but a fool." -
source *mywebpages.comcast.net/SupportCD/XPMyths.html
Reality - All it does is change your hash number - the OS is doing exactly the same thing it did before, and just saving the prefetch pages to a different file. It does not improve performance in any way. Ryan Myers of Microsoft's Windows Client Performance Team writes: "The /prefetch:# flag is looked at by the OS when we create the process - however, it has one (and only one) purpose. We add the passed number to the hash. Why? WMP is a multipurpose application and may do many different things. The DLLs and code that it touches will be very different when playing a WMV than when playing a DVD, or when ripping a CD, or when listening to a Shoutcast stream, or any of the other things that WMP can do. If we only had one hash for WMP, then the prefetch would only be correct for one such use having incorrect prefetch data would not be a fatal error - it'd just load pages into memory that'd never get used, and then get swapped back out to disk as soon as possible. Still, it's counterproductive. By specifying a /prefetch:# flag with a different number for each "mode" that WMP can do, each mode gets its own separate hash file, and thus we properly prefetch. (This behavior isn't specific to WMP - it does the same for any app.) This flag is looked at when we create the first thread in the process, but it is not removed by CreateProcess from the command line, so any app that chokes on unrecognized command line parameters will not work with it. This is why so many people notice that Kazaa and other apps crash or otherwise refuse to start when it's added. Of course, WMP knows that it may be there, and just silently ignores its existence. I suspect that the "add /prefetch:1 to make rocket go now" urban legend will never die, though." - Source - Source 2
Cleaning the Prefetch Folder
Myth - "Deleting the contents of the Prefetch folder improves performance."
Reality - "Every time you delete an application's Prefetch (.PF) file you will cripple that application's load time the next time you go to launch it. This can temporarily increase load times by as much as 100%. For one thing, XP will just re-create the Prefetch (.PF) trace files anyway; secondly, it trims the files if there's ever more than 128 of them so that it doesn't needlessly consume space. However you do not regain optimal application load times back until after the second time you launch the same application due to the Prefetch (.PF) trace file being re-created. Prefetch (.PF) trace files are not a cache and are not preloaded into memory upon windows startup. They are never even accessed until you launch an application. Only one Prefetch (.PF) trace file per application is created. There is never ANY reason to delete these files. Cleaning the Prefetch folder is actually a temporary self-inflicted unoptimization. Why you would want to deliberately hurt your PC's performance I have no idea." - Source - Source 2 - Source 3 - Source 4 - Source 5
Malware/Viruses - Some people irresponsibly recommend cleaning this folder due to possible Malware/Virus infection. Malware/Viruses can place an infected file(s) in any folder and the Prefetch folder is no different. Do these same people recommend deleting the contents of the Windows folder because it is a popular location to find an infected file(s)? Of course not, you simply clean or delete the infected file(s) not the contents of the folder. This Myth got started due to the indiscriminate nature of the Windows Prefetcher, which will Prefetch any executable file that you load or loads during Windows start up. Thus it is quite common on an infected machine to find a Prefetch (.PF) trace file in the Prefetch folder with the same name as an infected executable. These files are NOT Malware/Viruses. They are there to improve the load time, in this case ironically, of the Malware/Virus but do not contain any infected code. Once the associated infected executable is deleted, these Prefetch (.PF) trace files do nothing and will eventually automatically be cleaned by Windows.
Corrupted Files - Some people claim that Prefetch (.PF) trace files can get randomly "corrupted" and thus they need to be periodically deleted. Files do not get "corrupted" unless something is wrong with your computer. Any file corruption is a warning sign something is wrong with your system. Overclocking, using defective components like Memory and Harddrives and using FAT32 instead of the superior NTFS file system are common causes of file corruption. NTFS is very resilient to file corruption as compared to FAT32. When storing data to disk, NTFS records file I/O events to a special transaction log. If the system crashes or encounters an interruption, NTFS can use this log to restore the volume and prevent corruption from an abnormal program termination or system shutdown. NTFS doesn't commit an action to disk until it verifies the successful completion of the action. This precaution helps prevent corruption of an NTFS volume. NTFS also supports hot-fixing disk sectors, where the OS automatically blocks out bad disk sectors and relocates data from these sectors. This housecleaning happens in the background. An application attempting to read or write data on a hot-fixed area will never know the disk had a problem. Thus the solution is fixing the cause of the file corruption.
CCleaner - Finally the useless, performance slowing cleaning option "Old Prefetch data" was moved to the advanced section and is now not selected by default. Never select this option for cleaning as it will increase application and Windows load times. This option removes Prefetch files that are a few weeks old based on the NTFS last access date. Since Windows XP already cleans this folder at 128 entries, this is a useless option that will only reduce system performance. You should never delete a Prefetch file for any installed application since that would cripple it's load times. Just because a program was not used in a few weeks does not mean you want it to load as slow as possible when you do decide to use it. If you disable the NTFS last access date stamp then this option will delete the whole contents of the Prefetch folder after a few weeks, which will cripple Windows Boot and all application load times. The Prefetch folder is also ridiculously small so cleaning Prefetch files before the 128 limit will reclaim next to no disk space. This option clearly needs a warning to prevent people from unknowingly hurting their system performance. Anyone who claims this should be cleaned for ANY reason does not understand how Windows Prefetching works. - Source
Bad Advice - This bad advice to clean the prefetch folder is posted frequently on the Internet by people who do not understand how the Windows XP Prefetcher works. Their explanations are 100% inaccurate. - Bad Advice 1 - Bad Advice 2 - Bad Advice 3 - Bad Advice 4
EnablePrefetcher
[HKLM\SYSTEM\CurrentControlSet\Control\SessionManager\MemoryManagement\PrefetchParameters] "EnablePrefetcher"
Myth - "Setting any value higher then 3 to EnablePrefetcher will improve performance."
Reality - 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. This is a new feature in Windows XP which improves application load times and Windows boot times automatically. The slower your system and the larger an application, the more Prefetching helps. Even high end systems benefit from prefetching with large, slow loading applications, such as large games. By default Prefetching is enabled in Windows XP and already configured optimally. The following list describes the different possible values for the EnablePrefetcher registry key.
0 = Disabled
1 = Application launch prefetching enabled
2 = Boot prefetching enabled
3 = Applaunch and Boot enabled (Optimal and Default)
By default the Prefetcher is set to a value of 3 in Windows XP. Values such as 4, 5, 6 ect... do not exist and are thus useless. Leave this at the default value of 3 which is already optimal for maximum performance on both Windows XP Boot and initial application launches. - Source
Low Memory Systems - Recommendations to disable Prefetching on low memory systems (128 MB - 512 MB) is based on the fallacy that portions of application code are preloaded into memory before the application load is initiated during Windows startup. This is completely false and is spread by people who do not understand how Windows XP Prefetching works. The slower the system the more it will benefit from Prefetching. 64 MB systems will suffer due to insufficient RAM, reducing but not eliminating Window XP's prefetching benefits. 128 MB is the recommended minimum for optimal prefetching performance.
Boot Performance - Recommendations to set the EnablePrefetcher value to 2 to improve boot performance is based on the fallacy that portions of application code are preloaded into memory before the application load is initiated during Windows XP startup. This is completely false and is spread by people who do not understand how Windows XP Prefetching works. Only the files used during boot will be Prefetched. The Prefetch folder is not a cache. Windows XP will boot in the exact same amount of time with either value 2 or 3, the only difference with 2 is that now all of your initial application launches will not be Prefetched and thus load slower. The default value of 3 in no way negatively affects Windows XP boot times. Leave the value at 3 for optimal Windows XP boot and initial application launch times.
Enable Superfetch
[HKLM\SYSTEM\CurrentControlSet\Control\SessionManager\MemoryManagement\PrefetchParameters] "EnableSuperfetch"
Myth - "Adding EnableSuperfetch to the registry improves performance in Windows XP as it does in Windows Vista."
Reality - "This myth was started when the Inquirer irresponsibly ran a bogus letter without doing any fact checking. Windows internals guru Mark Russinovich said this won't work, the "Superfetch" string isn't even in the Windows XP kernel. You can confirm this yourself by checking with the strings.exe utility. This makes it impossible for it to do anything since no "Superfetch" command exists. Windows cannot execute a nonexistent command and will simply ignore it. Anyone who says this works is not only lying but a fool." -
source *mywebpages.comcast.net/SupportCD/XPMyths.html
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