A floppy disk that contains key system files from a PC-compatible operating system and that can boot, or start, the PC. A boot disk must be inserted in the primary floppy disk drive (usually drive A:) and is used when there is some problem with starting the PC from the hard disk, from which the computer generally boots. Also called: bootable disk. See also A:, boot2, boot drive, hard disk.
A disk that contains an operating system and can be used to boot a computer. Also called: startup disk. See also boot2, operating system.