Tuesday, August 17, 2010

Windows Prefetch

Windows Prefetch is a feature first introduced in Microsoft Windows XP aimed at helping Windows to load some sections of commonly run programs when the computer first loads. This was introduced in order to allow frequently run programs in Windows to load faster.

This simply means that each time a computer is switched on, Windows keeps track of how programs commonly open and saves the information in a Prefetch Folder. Each time your computer is switched on, Windows looks for these files in the Prefetch folder. This feature saves the time the user would wait for the computer to load programs the next time you turn on the computer.

When Windows system boots, a large number of files need to be read into memory and processed. Often, this includes loading different segments of the same file at different times. As a result, a significant amount of time is spent opening and accessing files multiple times, where a single access would be more efficient. The prefetcher works by watching what code and data is accessed during the boot process (including reads of the NTFS Master File Table), and recording a trace file of this activity. Future boots can then use the information recorded in this trace file to load code and data in a more optimal fashion. The boot prefetcher will continue to watch for such activity until 30 seconds after the user's shell has started, or until 60 seconds after all services have finished initializing, or until 120 seconds after the system has booted, whichever elapses first. Application prefetching works in a similar fashion, but is instead localized to a single application's startup. Only the first 10 seconds of activity are monitored.

References: Microsoft, Wikipedia

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