The ROM chip, RAM chips and CPU are all plugged into small sockets on the motherboard . These sockets can hold CD-ROM sound cards, FAX modem cards, video display boards, disk controller cards, networking boards and SCSI cards. These devices will be explained in more detail later. The case also includes the power supply transformer which converts normal household current to a much lower voltage that the motherboard can use. There are several disk storage devices inside, including the hard disk drive, the floppy disk drive and the CD-ROM drive.
Many computers users add a tape storage drive as well.
It's used to back up valuable data onto small cassette tapes.