A magnetic disk drive that (a) is often used in personal computer (PC) systems and in microcomputers, (b) usually includes several self-contained and sealed parts, such as a controller, a motor drive mechanism, a disk-holding mechanism, and a read-write head assembly, and (c) may be built-in or contained in removable cartridges, each with a storage capacity usually greater than 40 Mb (megabytes). See also  cartridge,  disk drive,  magnetic disk,  megabyte,  microcomputer,  personal computer,  read-write head,  storage capacity.