These quick and efficient drives hold all the data stored on your computer including the operating system as well as anything else you want to save or run on your computer. When purchasing a Hard Drive, it should be no slower than 7200RPM and be no smaller than 40GB and be a brand name like Maxtor or Western Digital. A Special Edition 80GB 7200RPM 8MB cache Hard Drive is a great investment. Below is an internal picture of a WD HDD.