Understanding Prefetch

As introduced earlier, Prefetching is a standard Windows performance optimization mechanism. It monitors the initial file access patterns of applications when they launch and stores this information in dedicated files. The next time the application runs, Windows can use this stored data to load necessary resources into memory more proactively, theoretically speeding up the startup time.

• Location: Prefetch data is stored as individual files (with a .pf extension) within the C:\Windows\Prefetch directory. Access usually requires administrator privileges.

• File Naming Convention: Each .pf file corresponds to a specific executable run from a specific path and follows the pattern: EXECUTABLENAME.EXE-HASH.pf.

  • EXECUTABLENAME.EXE: The name of the executable file that was launched (e.g., NOTEPAD.EXE, JAVAW.EXE).

  • HASH: An 8-character hexadecimal hash derived from the full path of the executable. This hashing ensures that running the same program (e.g., AnyDesk.exe) from different locations (like Downloads vs. Desktop) generates separate and distinct .pf files.

• Creation Trigger: Generally, a Prefetch file is created or updated only when an executable file (.exe) is launched.

  • Running non-executable files like .jar archives will typically update or create a Prefetch entry for the Java runtime environment (java.exe or javaw.exe) that executes the .jar.

  • Loading .dll files via injection or standard mechanisms might generate or update Prefetch entries for the host process responsible for loading the DLL (e.g., rundll32.exe, regsvr32.exe, dllhost.exe, or the injector application itself). Direct execution of DLLs is not standard, so they don't get their own primary .pf files.