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bootable diskA CD-ROM or DVD-ROM that contains its own operating system ready to load. PCs are typically configured to look for the OS on a CD or DVD first and then the hard disk or SSD. Except for earlier models, computers can also be booted from a flash memory-based USB drive (see USB drive).
System and Data Recovery
A bootable disk is used to recover a failed system when the OS on the internal storage drive cannot load. The OS on the bootable disk does not have to be the same version. However, it must support the file system on the storage drive so that the files can be examined and repaired. In addition, the OS on the bootable disk must contain the appropriate software drivers for all the peripherals that will be used in a recovery attempt. See file system.
If the operating system cannot be restored, the bootable disk allows valuable data files to be copied to an external drive. In the past, a compact version of DOS was often used as a bootable disk.
Install or Replace an Operating System
A bootable disk is also used to install a new operating system. By booting its own operating system (not necessarily the one being installed), it is able to format and write to the blank hard disk or SSD on a new computer. In addition, when replacing an existing operating system, it gives the installation program complete control of the computer. See LiveCD.