SuperFetch is a technology that pre-loads commonly used applications into memory to reduce their load times. It is based on the "prefetcher" function in Windows XP.
The intent is to improve performance in situations where running an anti-virus scan or back-up utility would result in otherwise recently-used information being paged out to disk, or disposed from in-memory caches, resulting in lengthy delays when a user comes back to their computer after a period of non-use.
SuperFetch also keeps track of what times of day those applications are used, which allows it to intelligently pre-load information that is expected to be used in the near future.
By default the necessary files are loaded into main memory, but using a feature called ReadyBoost, Windows Vista and Windows 7 can use alternate storage such as USB flash drives, thereby freeing up main memory. Although hard disks usually have higher data transfer rates, flash drives can be faster for small files or non-sequential I/O because of their short random seek times.