How does ReadyBoost work

ReadyBoost works by using flash memory such as a USB drive, SD card or CF (CompactFlash) card as a cache. The core idea of ReadyBoost is that a flash drive is capable of a much faster seek time than a typical magnetic hard disk (less than 1 ms), allowing it to return requests faster than reading files from a rotating hard disk. It also leverages the inherent advantage of multiple parallel sources from which to read data. Windows 7 enables the use of up to eight flash drives at once, allowing up to nine parallel sources and greatly reducing the access time required.

Are there any Disadvantages to ReadyBoost?

Since flash drives wear out after a finite (though very large) number of writes, ReadyBoost could eventually wear out the drive it uses—though this may take a long time, depending on various factors. According to Microsoft, the drive should be able to operate for at least ten years.