A disc that contains special, hidden startup files and other programmes to run a computer, usually specific to the operating system and version. Several types of boot discs are available to an average user, including a standard floppy boot disk, an emergency boot disk, and a bootable CD. Since most anti-virus programmes work best when they can gain complete access to the hard drive, it is important to use a boot disc when disinfecting a computer. In some cases, failure to use a boot disc prevents your anti-virus programmes from detecting and removing certain viruses from the computer.