A Microsoft Windows Vista feature for adding memory to a system using flash memory, such as a USB flash drive, to improve performance without having to add additional system memory. The flash memory device will work as an additional memory cache that the computer can access much more quickly than it can access data on the hard drive. When a removable memory device is inserted into a port, Windows Vista checks to see if its performance is fast enough to work with Windows ReadyBoost. If it's compatible you can then choose to use the memory device to speed up system performance. You also have the option to allocate all the drive to speed up performance or allocate only a portion and use the remainder for file storage. Despite the performance boost offered by Windows ReadyBoost, adding RAM is the best way to improve performance of your computer.