Compact disk-read only memory (CD-ROM) refers to a 4.75-inch, laser encoded, optical memory storage medium. Technologies include CD-ROM XA (extended architecture), CD-RW (rewritable), and CD-WO (write once).
Hard drives are integral, non-volatile, electronic data storage units inside computers. Traditionally, hard drives were hard-wired into computers. Removeable hard disks and drives are also available.