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El Torito (CD-ROM standard)
From Wikipedia, the free encyclopedia
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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 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.
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 needed]
- 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)