Cache- High-speed RAM is used as a buffer between the CPU and a hard drive. The cache retains recently accessed information to speed up subsequent access to the same data. When data is read from or written to disk, a copy is saved in a cache, along with the associated disk address. The cache monitors the addresses of subsequent read operations to see if the required data is already in the cache. If it is, the drive returns the data immediately. If it is not in the cache, than it is fetched from the disk and saved in the cache.