Prefetching was a performance feature introduced in Windows XP that monitored your system and anticipated the data that you might use in the near future. It then loaded (prefetched) that data into memory ahead of time. If that data was indeed what your system required, performance would increase because XP wouldn't have to fetch the data from your hard disk.

Windows Vista introduces a new and improved version of the Prefetcher: SuperFetch. This technology tracks the programs and data you use over time to create a kind of profile of your disk usage. Using the profile, SuperFetch can then make a much more educated guess about the data that you'll require and, like the Prefetcher, can then load that data into memory ahead of time for enhanced performance.

However, SuperFetch goes even further by taking advantage of Vista's new ReadyBoost technology. If you insert a 512MB (or larger) USB 2.0 Flash drive into your system, Vista displays the AutoPlay dialog box. If you click Speed Up My System Using Windows ReadyBoost, SuperFetch uses that drive's capacity as storage for the SuperFetch cache. This frees up the system RAM that SuperFetch would otherwise use, which should result in an automatic (and probably quite dramatic) performance boost. Not only that, but you still get an extra performance nudge from SuperFetch itself because even though data access via the Flash drive is slower than with system RAM, it's still many times faster than even the fastest hard drive.

You can also control the amount of storage space that SuperFetch uses on the Flash drive. Select Start, Computer; right-click the Flash drive; and then click Properties to open the device's property sheet. In the Memory tab, click Use This Device to let SuperFetch access the Flash memory and then use the slider to set the maximum amount of memory SuperFetch can use.