"El Torito" Bootable CD-ROM Format Specification Version 1.0
Phoenix Technologies / IBM
Contents
1.0 OVERVIEW 3
1.1 Scope 3
1.2 Notation and Conventions 3
1.3 Introduction 3
1.4 Implementation Options 4
1.5 Definition of Terms 5
2.0 ISO-9660 AND THE BOOTING CATALOG 6
2.1 Validation Entry 6
2.2 Initial/Default Entry 6
2.3 Section Header 6
2.4 Section Entry 6
2.5 Section Entry Extension 7
3.0 THE INT 13 ACCESSIBLE IMAGE 11
4.0 INT 13 AND CD-ROMS 11
4.1 INT 13 Function 08 11
4.2 INT 13 Function 48 11
4.3 INT 13 and Booting 11
4.4 Boot Entry Selection 12
5.0 CD BOOT PROCEDURES 13
5.1 Floppy Booting 13
5.2 Hard Disk Booting 13
5.3 No Emulation Booting 13
5.4 System Optimization 13
6.0 NEW INT 13 FUNCTIONS 14
6.1 INT 13 Function 4A - Initiate Disk Emulation 14
6.2 INT 13 Function 4B - Terminate Disk Emulation 14
6.3 INT 13 Function 4C - Initiate Disk Emulation & Boot 15
6.4 INT 13 Function 4D - Return Boot Catalog 15
1.0 Overview
This specification defines how makers of CD-ROMs can package several "images"
of floppy and hard disks on a single CD with the ability to catalog these images
and to selectively boot from any single image.
The possibility of booting a PC from a CD ROM has raised several possibilities,
including:
1. Self-configuring CD-ROMs that manage their own resources, including
operating systems and drivers
2. The embedding of multiple operating systems and drivers on the same
CD-ROM for a variety of applications, e.g., multi-language
3. The ability of the end user to select which operating system to boot
4. Copy protection for the CD ROM software and data
To accomplish this facility, there are currently two available technologies:
1. DOS-based drivers (e.g., SCSI or ATAPI)
2. The system BIOS.
Attempting to use DOS-based drivers (e.g., SCSI or ATAPI) to boot from a CD ROM
creates a number of problems such as resource conflicts and inordinate use of
memory. The BIOS, however, avoids these problems and offers other advantages,
including:
1. Can boot from a variety of operating systems by accessing a Boot Catalog
on the CD-ROM.
2. Offers the choice of configuring the CD ROM as a hard disk (C: or D:) or
floppy (A:).
3. Renames existing drives when necessary.
4. Uses existing BIOS technology (Logical Block Access) to access code and
data.
5. Compatible with all DOS and Windows applications using INT 13 functions.
Using the BIOS to boot from the CD ROM requires using the available system
header on the CD ROM
1.1 Scope
This document describes in detail how to format a CD-ROM from which you can boot
a suitably-equipped computer system. It assumes you are familiar with standard
BIOS INT 13 functions, ISO document number 9660, IBM/Microsoft INT 13 Extensions
Dated 9/92, Version 1.0 of the Enhanced Disk Drive Specification (authored by
Phoenix), and ATAPI.
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