El Torito (CD-ROM standard)

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Optical disc authoring

Optical disc Optical disc image Recorder hardware Authoring software Recording technologies Recording modes Packet writing
Optical media types
Laserdisc Compact Disc/CD-ROM: CD-R, CD-RW DVD: DVD-R, DVD-R DL, DVD+R, DVD+R DL, DVD-RW, DVD+RW, DVD+RW DL, DVD-RAM Blu-ray Disc: BD-R, BD-RE HD DVD: HD DVD-R
Standards
Rainbow Books File systems ISO 9660 Joliet Rock Ridge Amiga extensions to Rock Ridge El Torito Apple ISO9660 Extensions Universal Disk Format Mount Rainier

The El Torito Bootable CD Specification is an extension to the ISO 9660 CD-ROM specification. It is designed to allow a computer to boot from a CD-ROM. It was first issued in January 1995 as a joint proposal by IBM and BIOS manufacturer Phoenix Technologies.

A modern PC BIOS will search for boot code on a ISO 9660 CD according to the El Torito specification. If the CD contains bootable code, the BIOS will assign a BIOS drive number to the CD drive. The drive number assigned is either 80 (hard disk emulation), 00 (floppy disk emulation) or an arbitrary number if the BIOS should not provide emulation.

Emulation allows older operating systems to be booted off a CD, by making it appear to them as if they were booted off a hard or floppy disk. Newer operating systems do not require emulation to boot; all that is needed is an appropriate boot loader such as ISOLINUX.

If you need to boot from a CD on an old PC without an El Torito-capable BIOS you can try Smart Boot Manager, which has a standalone El Torito stack.

[edit] Name origin

According to legend, the El Torito CD/DVD extension to ISO 9660 gained its name because its design originated in an El Torito restaurant in Irvine, California.