ReadyBoost whose code name is "Extended Cache" is the name of a disk caching technology included in Windows Vista and Windows 7 from Microsoft.
ReadyBoost makes computers use flash memory devices, like USB drives, memory cards (Secure Digital Card, Compact Flash, etc..), among others, to improve the overall performance of a computer.
Windows Vista and Windows 7 takes advantage of compatible memory devices that are inserted into the computer by using it to cache information, with a reading performance about 10 times faster than a traditional hard drive. Nonetheless, as flash memory devices are slower for sequential input / output operations, to maximize the system performance, such operations are redirected to the hard disk. With Readyboost, you notice considerable improvements during heavy tasks and repetitive disk access. This includes when there is little available memory and tasks such as switching between users.