El Torito (CD-ROM standard)

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Optical disc authoring v • d • e
Optical disc Optical disc image Optical disc drive Optical disc authoring Authoring software Recording technologies Recording modes Packet writing
Optical media types
Laserdisc (LD), Video Single Disc (VSD) Compact Disc (CD): Red Book, 5.1 Music Disc, SACD, PhotoCD, CD-R, CD-ROM, CD-RW, CD Video (CDV), Video CD (VCD), SVCD, CD+G, CD-Text, CD-ROM XA, CD-i MiniDisc (MD) (Hi-MD) DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-RW, DVD+RW, DVD-RW DL, DVD+RW DL, DVD-RAM, DVD-D Ultra Density Optical (UDO) Universal Media Disc (UMD) HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM, HD DVD-ROM Blu-ray Disc (BD): BD-R, BD-RE
Standards
Rainbow Books File systems ISO 9660 Joliet Rock Ridge El Torito Apple ISO 9660 Extensions Universal Disk Format (ISO 9660) (UDF) Mount Rainier
Further reading
History of optical storage media High definition optical disc format war

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 announced in November 1994^[1] and 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 from a CD, by making it appear to them as if they were booted from 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.

Contents 1 Name origin 2 See also 3 References 4 External links

[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.^[2] The initial two authors were Curtis Stevens, of Phoenix Technologies, and Stan Merkin, of IBM.^[3]

[edit] See also

• Booting
• Boot disk
• Live CD
• EFI

[edit] References

1. ^ Phoenix Technologies Ltd. (1994-11-11). "Phoenix announces bootable CD-ROM specification; Specification developed jointly by Phoenix and IBM". Press release. Retrieved on 2008-01-31.
2. ^ Parker, Dana J., “Fresh Tortillas and CD-ROM Standards: The El Torito Bootable CD-ROM Specification”, CD-ROM Professional 8 (7), <http://web.archive.org/web/19991008045553/http://www.cdpage.com/Compact_Disc_Variations/danaboot.html>. Retrieved on 31 January 2008 
3. ^ Ibid.

[edit] External links

• The "El Torito" Bootable CD-ROM Format Specification, Version 1.0 (PDF)
• ISOLINUX source code (see isolinux.asm line 294 onward)
• Ralf Brown's interrupt list (see int 13h in interrup.b, esp. functions 4a to 4d)
• EL Torito Specification Supplement, discusses shortcomings of the standard