– Long-term, nonvolatile storage

– Large, inexpensive, slow level in the storage hierarchy

–A magnetic disk consist of a collection of platters (1to 20 per disk) that rotate on a spindle.

–Disk surface divided into tracks (1000 to 4800 per platter).

–Tracks are divided into sectors (64 per track), which are the smallest unit that can be read or written.

• Up to 10,000 rpm