El Torito (CD-ROM standard)

El Torito (CD-ROM standard)

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 [cite press release
title = Phoenix announces bootable CD-ROM specification; Specification developed jointly by Phoenix and IBM
publisher = Phoenix Technologies Ltd.
date = 1994-11-11
url = http://www.thefreelibrary.com/Phoenix+announces+bootable+CD-ROM+specification%3b+Specification...-a015922225
accessdate = 2008-01-31 ] 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.

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. [Citation | last = Parker
first = Dana J.
title = Fresh Tortillas and CD-ROM Standards: The El Torito Bootable CD-ROM Specification
periodical = CD-ROM Professional
volume = 8
issue = 7
url = http://web.archive.org/web/19991008045553/http://www.cdpage.com/Compact_Disc_Variations/danaboot.html
archiveurl = http://web.archive.org/web/19991008045553/http://www.cdpage.com/Compact_Disc_Variations/danaboot.html
accessdate = 2008-01-31 ] The initial two authors were Curtis Stevens, of Phoenix Technologies, and Stan Merkin, of IBM. ["Ibid."]

ee also

*Booting
*Boot disk
*Live CD

References

External links

* [http://www.phoenix.com/NR/rdonlyres/98D3219C-9CC9-4DF5-B496-A286D893E36A/0/specscdrom.pdf The "El Torito" Bootable CD-ROM Format Specification, Version 1.0] (PDF)
* [http://www.kernel.org/git/?p=boot/syslinux/syslinux.git;a=blob;hb=HEAD;f=isolinux.asm ISOLINUX source code] (see isolinux.asm line 294 onward)
* [http://www.cs.cmu.edu/afs/cs.cmu.edu/user/ralf/pub/WWW/files.html Ralf Brown's interrupt list] (see int 13h in interrup.b, esp. functions 4a to 4d)
* [http://littlesvr.ca/isomaster/eltoritosuppl.php EL Torito Specification Supplement] , discusses shortcomings of the standard


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