How does it work?
Windows Vista introduces Windows ReadyBoost, a new concept in adding memory to a system. You can use non-volatile flash memory, such as that on a universal serial bus (USB) flash drive, to improve performance without having to add additional memory "under the hood."

The flash memory device serves as an additional memory cache - that is, memory that the computer can access much more quickly than it can access data on the hard drive. Windows ReadyBoost relies on the intelligent memory management of Windows SuperFetch and can significantly improve system responsiveness.