Prefetch Files

• A prefetch is a Windows file that indexes information of programs you usually use. When you run Microsoft Word, it needs to load several things like DLL files and other drivers that it depends on before it is launched. These files are scattered in different directories, which Windows has to fetch every time you run Microsoft Word. The prefetch files speed up this process by indexing the information needed to launch programs you typically use. Instead of locating every directory for the drivers needed to launch Microsoft Word, it simply checks the prefetch file then proceeds to launch the program.
  
  

What Prefetch File Contains

• The prefetch file is named similarly to the application it is set to launch. The information it contains includes the executable associated with launching the program, the directory location where the process is located, the last time you ran the program, and how many times you've launched the program since the prefetch file was created. The prefetch also contains all the DLLs and drivers used in launching the program and where they can be found. The indexing process used by the prefetch makes it easy for Windows to launch commonly used applications.
  
  

Location

• The prefetch folder is located in C:\Windows\Prefetch. Windows first checks this folder every time it is set to launch an application. If a prefetch is found here, Windows uses the information contained in the prefetch to load the application faster.
  
  

How Windows Know What To Prefetch

• Windows uses its Cache Manager to know what it should prefetch, which monitors and traces all the files that are accessed and launched during start up and the first 10 seconds when you're launching an application. It is during these first 10 seconds that your application loads the necessary DLLs and drivers to launch itself and the Cache Manager collects this information to create the prefetch file.
  
  

Further Enhancement

• To make loading applications even faster, especially during start up, a configuration file called Layout.ini located in the prefetch folder is created, which lists all the files loaded from start up until an application is launched. It is listed chronologically from the very first file used during start up to the last one used before the configuration file was created. The Layout.ini is usually created and updated every three days by the task scheduler.
  
  

Considerations

• Prefetch files are safe to delete since Windows only uses them to speed up the loading of an application. The advantage of the prefetch is felt more on slower systems. Faster systems with higher memory may not easily notice the difference of a prefetch when launching an application. If you delete a prefetch, it will still be created the next time you launch an application unless you disable the prefetch.
  
  

Disabling Prefetch

• Prefetch can only be disabled by editing the registry. To do this, type on the Run box: regedit. This opens the registry editor. Proceed to:
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters and find the parameter: EnablePrefetcher. Set the value to 0. This effectively disables the prefetch.