Windows prefetch file Windows uses the .PF file extension for storing prefetch trace files. Since Windows XP Microsoft has used the prefetcher memory management utility to speed up the start-up of Windows. Put very basically whilst booting up Windows access different parts of the same files at different points in the process. Reloading each of these files every time Windows needs to access a different section takes time, and hence the prefetcher utility helps by keeping a record, in the .pf trace files, of which files are accessed and when, and then seeks to use this information to expedite the boot up process in future.