A bootable CD is usually needed when you need to boot from any other media without booting the computer from the hard disk drive. For example: 1. When loading the operating system. 2. When repairing the operating system. 3. To fix the problem of hard disk drive. 4. When loading the operating system from the hard disk drive, any work can be done perfectly. For example: in the case of live antivirus. That is, in the case of virus removal perfectly. 5. To create a customized operating system installer CD, the CD will have many features besides the operating system installer.