SuperFetch

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SuperFetch is a performance enhancement introduced in Microsoft Windows Vista to reduce the time necessary to launch applications. An expanded version of the Prefetch files found in Windows XP, they record usage scenarios and load resources into memory before they are needed. Those resources can be loaded into physical memory and extra memory provided by ReadyBoost.

Data for SuperFetch is gathered by the %SystemRoot%\System32\Sysmain.dll, part of the Service Host process, %SystemRoot%\System32\Svchost.exe, and stored in a series of files in the %SystemRoot%\Prefetch directory [1]. These files appear to start with the prefix Ag and have a .db extension. The format of these files is not known, but they are not actually databases [2]. Some information can be gleaned from these files by searching for Unicode strings in them.

The SuperFetch feature is seeded with some basic usage patterns when the operating system is installed [3].

Because SuperFetch appears to leave a system with no available memory, some users turn it off to create the appearance of having more free memory. The feature can be disabled by the user by changing the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnableSuperfetch Registry key [4]. A value of zero disables SuperFetch, one enables it for booting only, two for applications, and three for both applications and boot. This setting can also be changed using the Services console, services.msc [5].

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