[1] It is a component of the Memory Manager that can speed up the Windows boot process and shorten the amount of time it takes to start up programs.
SuperFetch attempts to accelerate application launch times by monitoring and adapting to application usage patterns over periods of time, and caching the majority of the files and data needed by them into memory in advance so that they can be accessed very quickly when needed.
ReadyBoost (when enabled) uses external memory like a USB flash drive to extend the system cache beyond the amount of RAM installed in the computer.
ReadyBoost also has a component called ReadyBoot that replaces the Prefetcher for the boot process if the system has 700 MB or more of RAM.
Future boots can then use the information recorded in this trace file to load code and data in a more efficient fashion (i.e. by re-ordering disk reads to minimise or eliminate the need to access the same file multiple times thus minimising disk head movements).
To further improve access times, the Task Scheduler calls Windows Disk Defragmenter every three days.
[1]: 461–462 The processed result is stored in Layout.ini in the Prefetch directory, and is subsequently passed to the Disk Defragmenter, instructing it to re-order those files into sequential positions on the physical hard drive.