《计算机维护维修 Computer Load & Repair》课程教学资源（文献资料）“El Torito” Bootable CD-ROM Format Specification Version 1.0.pdf_大学文库

“ “ El El Torito Torito ” ” Bootable Bootable Bootable Bootable CD-ROM CD-ROM Format Format Specification Specification Specification Specification Version Version Version Version 1.0 1.0 September September September September 26, 26, 2004 2004 Curtis E. Stevens Stan Merkin (Formerly of IBM, Currently with DELL) Phoenix Technologies IBM 2575 McCabe Way 1000 NW 51 st Irvine, Ca. 92714 BocaRaton, Fl. 33431 Phone: (714) 440-8330 Phone: (407) 443-3264 Fax: (714) 440-8300 Fax: (407) 982-8823 curtis_stevens@bannet.ptltd.com THIS THIS SPECIFICATION SPECIFICATION SPECIFICATION SPECIFICATION IS IS MADE MADE AVAILABLE AVAILABLE AVAILABLE AVAILABLE WITHOUT WITHOUT WITHOUT WITHOUT CHARGE CHARGE FOR FOR USE USE IN IN DEVELOPING DEVELOPING DEVELOPING DEVELOPING COMPUTER COMPUTER COMPUTER COMPUTER SYSTEMS SYSTEMS SYSTEMS SYSTEMS AND AND CD-ROM CD-ROM DRIVES. DRIVES. DRIVES. DRIVES. THE THE DEVELOPERS DEVELOPERS DEVELOPERS DEVELOPERS OF OF THIS THIS DOCUMENT DOCUMENT DOCUMENT DOCUMENT MAKE MAKE NO NO REPRESENTATION REPRESENTATION REPRESENTATION REPRESENTATION OR OR WARRANTY WARRANTY WARRANTY WARRANTY REGARDING REGARDING REGARDING REGARDING THIS THIS SPECIFICATION SPECIFICATION SPECIFICATION SPECIFICATION OR OR ANY ANY ITEM ITEM DEVELOPED DEVELOPED DEVELOPED DEVELOPED BASED BASED ON ON THIS THIS SPECIFICATIO SPECIFICATIO SPECIFICATIO SPECIFICATIO N, N, AND AND THEY THEY DISCLAIM DISCLAIM DISCLAIM DISCLAIM ALL ALL EXPRESS EXPRESS EXPRESS EXPRESS AND AND IMPLIED IMPLIED IMPLIED IMPLIED WARRANTIES, WARRANTIES, WARRANTIES, WARRANTIES, INCLUDING INCLUDING INCLUDING INCLUDING BUT BUT NOT NOT LIMITED LIMITED LIMITED LIMITED TO TO THE THE IMPLIED IMPLIED IMPLIED IMPLIED WARRANTIES WARRANTIES WARRANTIES WARRANTIES OF OF MERCHANTABILITY, MERCHANTABILITY, MERCHANTABILITY, MERCHANTABILITY, FITNESS FITNESS FITNESS FITNESS FOR FOR A A PARTICULAR PARTICULAR PARTICULAR PARTICULAR PURPOSE PURPOSE PURPOSE PURPOSE AND AND FREEDOM FREEDOM FREEDOM FREEDOM FROM FROM INFRINGEMENT. INFRINGEMENT. INFRINGEMENT. INFRINGEMENT. WITHOUT WITHOUT WITHOUT WITHOUT LIMITING LIMITING LIMITING LIMITING THE THE GENERALITY GENERALITY GENERALITY GENERALITY OF OF THE THE FOREGOING, FOREGOING, FOREGOING, FOREGOING, THE THE DEVELOP DEVELOP DEVELOP DEVELOP ERS ERS OF OF THIS THIS DOCUMENT DOCUMENT DOCUMENT DOCUMENT MAKE MAKE NO NO WARRANTY WARRANTY WARRANTY WARRANTY OF OF ANY ANY KIND KIND THAT THAT ANY ANY ITEM ITEM DEVELOPED DEVELOPED DEVELOPED DEVELOPED BASED BASED ON ON THIS THIS SPECIFICATION SPECIFICATION SPECIFICATION SPECIFICATION WILL WILL NOT NOT INFRINGE INFRINGE INFRINGE INFRINGE ANY ANY COPYRIGHT, COPYRIGHT, COPYRIGHT, COPYRIGHT, PATENT, PATENT, PATENT, PATENT, TRADE TRADE SECRET SECRET OR OR OTHER OTHER INTELLECTUAL INTELLECTUAL INTELLECTUAL INTELLECTUAL PROPERTY PROPERTY PROPERTY PROPERTY RIGHT RIGHT OF OF ANY ANY PERSON PERSON OR OR ENTITY ENTITY IN IN ANY ANY COUNTRY. COUNTRY. COUNTRY. COUNTRY. USE USE OF OF THIS THIS SPECIFICA SPECIFICA SPECIFICA SPECIFICA TION TION FOR FOR ANY ANY PURPOSE PURPOSE PURPOSE PURPOSE IS IS AT AT THE THE RISK RISK OF OF THE THE PERSON PERSON OR OR ENTITY ENTITY USING USING IT. IT. version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 2 Contents 1.0 1.0 OVERVIEW OVERVIEW OVERVIEW OVERVIEW 1.1 1.1 Scope Scope 1.2 1.2 Notation Notation Notation Notation and and Conventions Conventions Conventions Conventions 1.3 1.3 Introduction Introduction Introduction Introduction 1.4 1.4 Implementation Implementation Implementation Implementation Options Options Options Options 1.5 1.5 Definition Definition Definition Definition of of Terms Terms 2.0 2.0 ISO-9660 ISO-9660 ISO-9660 ISO-9660 AND AND THE THE BOOTING BOOTING BOOTING BOOTING CATALOG CATALOG CATALOG CATALOG 2.1 2.1 Validation Validation Validation Validation Entry Entry 2.2 2.2 Initial/Default Initial/Default Initial/Default Initial/Default Entry Entry 2.3 2.3 Section Section Section Section Header Header 2.4 2.4 Section Section Section Section Entry Entry 2.5 2.5 Section Section Section Section Entry Entry Extension Extension Extension Extension 3.0 3.0 THE THE INT INT 13 13 ACCESSIBLE ACCESSIBLE ACCESSIBLE ACCESSIBLE IMAGE IMAGE 4.0 4.0 INT INT 13 13 AND AND CD-ROMS CD-ROMS CD-ROMS CD-ROMS 4.1 4.1 INT INT 13 13 Function Function Function Function 08 08 4.2 4.2 INT INT 13 13 Function Function Function Function 48 48 4.3 4.3 INT INT 13 13 and and Booting Booting Booting Booting 4.4 4.4 Boot Boot Entry Entry Selection Selection Selection Selection 5.0 5.0 CD CD BOOT BOOT PROCEDURES PROCEDURES PROCEDURES PROCEDURES 5.1 5.1 Floppy Floppy Booting Booting Booting Booting 5.2 5.2 Hard Hard Disk Disk Booting Booting Booting Booting 5.3 5.3 No No Emulation Emulation Emulation Emulation Booting Booting Booting Booting 5.4 5.4 System System Optimization Optimization Optimization Optimization 6.0 6.0 NEW NEW INT INT 13 13 FUNCTIONS FUNCTIONS FUNCTIONS FUNCTIONS 6.1 6.1 INT INT 13 13 Function Function Function Function 4A 4A - - Initiate Initiate Initiate Initiate Disk Disk Emulation Emulation Emulation Emulation 6.2 6.2 INT INT 13 13 Function Function Function Function 4B 4B - - Terminate Terminate Terminate Terminate Disk Disk Emulation Emulation Emulation Emulation 6.3 6.3 INT INT 13 13 Function Function Function Function 4C 4C - - Initiate Initiate Initiate Initiate Disk Disk Emulation Emulation Emulation Emulation & & Boot Boot 6.4 6.4 INT INT 13 13 Function Function Function Function 4D 4D - - Return Return Boot Boot Catalog Catalog Catalog Catalog

附件2-6：BM可引导光盘格式 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 ATAPD)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.. 1.2 Notation and Conventions All numbers in this document are hexadecimal unless otherwise specified.All reserved or unused bytes are assumed to be zero.All character strings are padded to their full length with hex zeros.All word,double word and quad word values listed in this spec are in"Little Indian"(Intel)format. 1.3 Introduction ATAPI-compliant IDE as well as SCSI CD-ROM drives can optionally provide new boot capabilities for personal computer manufacturers and users.In the past IBM and compatible personal computers would first attempt to boot from the floppy drive and if no floppy was present,from the hard disk. This specification explains how the BIOS boot procedure can be enhanced to support a new medium,the CD-ROM.The CD-ROM is a removable media type,much like a floppy,but with the capacity of a hard disk. Version 1.0 Copyright1994 Phoenix Technologies and IBM All Rights Reserved. Page 3

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 3 1.0 1.0 Overview Overview Overview 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 SCSI or ATAPI) 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 1.1 Scope 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.. 1.2 1.2 Notation Notation Notation Notation and and Conventions Conventions Conventions Conventions All numbers in this document are hexadecimal unless otherwise specified. All reserved or unused bytes are assumed to be zero. All character strings are padded to their full length with hex zeros. All word, double word and quad word values listed in this spec are in “Little Indian” (Intel) format. 1.3 1.3 Introduction Introduction Introduction Introduction ATAPI-compliant IDE as well as SCSI CD-ROM drives can optionally provide new boot capabilities for personal computer manufacturers and users. In the past IBM and compatible personal computers would first attempt to boot from the floppy drive and if no floppy was present, from the hard disk. This specification explains how the BIOS boot procedure can be enhanced to support a new medium, the CD-ROM. The CD-ROM is a removable media type, much like a floppy, but with the capacity of a hard disk

附件2-6：BM可引导光盘格式 Maintaining compatibility with current software requires using INT 13 calling conventions but providing an entirely new device interface.INT 13 places some restrictions on the information which a CD-ROM contains and also provides several new options for booting a system.The following is a list of new system capabilities and constraints: 1.The CD-ROM may boot as the A drive or the C drive. 2.If the CD-ROM boots as the A,drive it will contain a 1.2M,1.4M or 2.88M floppy image 3. If the CD-ROM boots as the A drive the systems normal A drive will become the B drive.If the system has a B drive it will become inaccessible. 4. If the CD-ROM boots as the C drive,it replaces the C drive. 5. No device drivers are necessary for applications which use the INT 13 interface.This means that normal MS-DOS compatible software can access the CD-ROM without a device driver.Some OS software,such as Windows,can be configured to use INT 13 giving the user immediate benefits from his CD. 6. Formatting a portion of the CD ROM as a"write protected"hard disk is an easy method of copy-protecting off- the-shelf software as well as allowing MS-DOS to function normally. 7.1 You can also copy-protect the non-disk-formatted portions of the CD ROM by embedding special CD-ROM drivers on the CD. 1.4 Implementation Options Adding CD-ROM booting to a system will also require changes to the"SETUP"user interface.Many systems allow the following boot options. A:then C: C:then A: C:only CD-ROM booting now adds several new possibilities.The table below is a complete list: A:then CD ROM then C: CD ROM then A:then C: CD ROM then C:then A: C:then A:then CD ROM CD ROM only Many systems will not require all of these options,but it is necessary to give the user a CD-ROM boot disable capability. The ability to disable CD-ROM booting is required because there has been no standard for using the first few sectors of the CD.In the event that random data causes the system to find a valid"Validation Entry"on a non-compliant CD the user must have the recourse of disabling the boot capability. If the end-user selects one of the Boot CD-ROM options on the Setup Menu,and if during POST the BIOS detects the presence of a CD-ROM drive,INT 19 at the end of POST will then attempt to load the operating system using the boot sequence specified in Setup. To accomplish this,the installable Boot CD ROM feature makes available one of two INT 19 functions: 1. Single-Image INT 19.This feature,if instructed to boot from the CD ROM,does the following: a.Accesses the Booting Catalog in the CD-ROM header(See below). b.Verifies the existence of a boot image on the CD ROM. c. Reads the Initial/Default Entry(See below)and boots from the disk image specified in this entry. Single-Image INT 19 knows nothing about multiple-images,nor does it know about their possible entries listed in the Booting Catalog. 2.Multiple-Image INT 19.This feature,if instructed to boot from the CD ROM,does the following: a.Accesses the Booting Catalog in the CD-ROM header. b.Verifies the existence of a boot image on the CD ROM Version 1.0 Copyright 1994 Phoenix Technologies and IBM All Rights Reserved. Page 4

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 4 Maintaining compatibility with current software requires using INT 13 calling conventions but providing an entirely new device interface. INT 13 places some restrictions on the information which a CD-ROM contains and also provides several new options for booting a system. The following is a list of new system capabilities and constraints: 1. The CD-ROM may boot as the A drive or the C drive. 2. If the CD-ROM boots as the A, drive it will contain a 1.2M, 1.4M or 2.88M floppy image. 3. If the CD-ROM boots as the A drive the systems normal A drive will become the B drive. If the system has a B drive it will become inaccessible. 4. If the CD-ROM boots as the C drive, it replaces the C drive. 5. No device drivers are necessary for applications which use the INT 13 interface. This means that normal MS-DOS compatible software can access the CD-ROM without a device driver. Some OS software, such as Windows, can be configured to use INT 13 giving the user immediate benefits from his CD. 6. Formatting a portion of the CD ROM as a “write protected” hard disk is an easy method of copy-protecting offthe-shelf software as well as allowing MS-DOS to function normally. 7. You can also copy-protect the non-disk-formatted portions of the CD ROM by embedding special CD-ROM drivers on the CD. 1.4 1.4 Implementation Implementation Implementation Implementation Options Options Options Options Adding CD-ROM booting to a system will also require changes to the “SETUP” user interface. Many systems allow the following boot options. A: then C: C: then A: C: only CD-ROM booting now adds several new possibilities. The table below is a complete list: A: then CD ROM then C: CD ROM then A: then C: CD ROM then C: then A: C: then A: then CD ROM CD ROM only Many systems will not require all of these options, but it is necessary to give the user a CD-ROM boot disable capability. The ability to disable CD-ROM booting is required because there has been no standard for using the first few sectors of the CD. In the event that random data causes the system to find a valid “Validation Entry” on a non-compliant CD the user must have the recourse of disabling the boot capability. If the end-user selects one of the Boot CD-ROM options on the Setup Menu, and if during POST the BIOS detects the presence of a CD-ROM drive, INT 19 at the end of POST will then attempt to load the operating system using the boot sequence specified in Setup. To accomplish this, the installable Boot CD ROM feature makes available one of two INT 19 functions: 1. Single-Image Single-Image Single-Image Single-Image INT INT 19 19 . This feature, if instructed to boot from the CD ROM, does the following: a. Accesses the Booting Booting Booting Booting Catalog Catalog Catalog Catalog in the CD-ROM header (See below). b. Verifies the existence of a boot image on the CD ROM. c. Reads the Initial/Default Initial/Default Initial/Default Initial/Default Entry Entry (See below) and boots from the disk image specified in this entry. Single-Image INT 19 knows nothing about multiple-images, nor does it know about their possible entries listed in the Booting Catalog. 2. Multiple-Image Multiple-Image Multiple-Image Multiple-Image INT INT 19 19 . This feature, if instructed to boot from the CD ROM, does the following: a. Accesses the Booting Catalog in the CD-ROM header. b. Verifies the existence of a boot image on the CD ROM

附件2-6：BM可引导光盘格式 c. Boots from either the image specified in the Initial/Default Entry or from one of the other images listed in Section Headers and Section Entries (See below)that follow the Initial/Default entry.The selection of which image to boot from depends on Selection Criteria determined by the OEM(See below). Normal CD-ROM Single Boot-Image Multiple Boot-Image Configuration Configuration Configuration Sector 0 Bootable System System Disk Image (Unused） (Unused) Sector 16 Primary Volume Descriptor Sector 17 System Volume Boot Record Volume Descriptor (Unused) Descriptors Primary Volume Descriptor CD-ROM Boot Record Volume Descriptor Image Set Terminator Volume Descriptor Booting Catalog Set Terminator Volume Descriptor CD-ROM Initial/Default Entry Image Booting Catalog Initial/Default Entry Bootable Boot Entry Disk Image Boot Entry Boot Entry CD-ROM Bootable Image Disk Image CD-ROM Bootable Image Disk Image Figure 1.Three types of CD-ROM configuration: 1.The Normal CD-ROM configuration is not bootable,uses Root Directory and CD-ROM drivers to access CD- ROM images. 2. A BIOS with Single Boot-Image capability accesses the Initial/Default Entry to access a single bootable disk image.After loading the operating system,the system can revert to standard CD-ROM drivers and the Root Directory to access CD-ROM images. 3.A BIOS with Multiple Boot-Image capability can access any one of a number of Bootable Disk Images listed in the Booting Catalog.After loading the operating system,the system can access other items in the disk image with standard INT 13 calls or return to normal access of CD-ROM images using CD-ROM drivers and the Root Directory 1.5 Definition of Terms For the remainder of this document the following definitions apply: Seetor-Is a sector of data on a CD.This is in all cases 800 bytes. Virtual Sector-Is a sector of data on an emulated device.This document only addresses 200 byte device(for emulation) Virtual Disk-A series of sectors on the CD which INT 13 presents to the system as a drive with 200 byte virtual sectors. There are 4 virtual sectors found in each"sector"on a CD. Version 1.0 Copyright1994 Phoenix Technologies and IBM All Rights Reserved. Page 5

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 5 c. Boots from either the image specified in the Initial/Default Entry or from one of the other images listed in Section Section Section Section Headers Headers Headers Headers and Section Section Section Section Entries Entries Entries Entries (See below) that follow the Initial/Default entry. The selection of which image to boot from depends on Selection Selection Selection Selection Criteria Criteria Criteria Criteria determined by the OEM (See below). System (Unused) Normal CD-ROM Configuration CD-ROM Image CD-ROM Image Descriptors Volume Multiple Boot-Image Configuration Booting Catalog Initial/Default Entry Boot Entry Boot Entry Boot Entry Bootable Disk Image Bootable Disk Image System (Unused) Bootable Disk Image Set Terminator Volume Descriptor Primary Volume Descriptor Boot Record Volume Descriptor Sector 0 Sector 16 Single Boot-Image Configuration Booting Catalog CD-ROM Image CD-ROM Image Initial/Default Entry Bootable Disk Image System (Unused) Set Terminator Volume Descriptor Primary Volume Descriptor Boot Record Volume Descriptor Sector 17 Figure 1. Three types of CD-ROM configuration: 1. The Normal CD-ROM configuration is not bootable, uses Root Directory and CD-ROM drivers to access CDROM images. 2. A BIOS with Single Boot-Image capability accesses the Initial/Default Entry to access a single bootable disk image. After loading the operating system, the system can revert to standard CD-ROM drivers and the Root Directory to access CD-ROM images. 3. A BIOS with Multiple Boot-Image capability can access any one of a number of Bootable Disk Images listed in the Booting Catalog. After loading the operating system, the system can access other items in the disk image with standard INT 13 calls or return to normal access of CD-ROM images using CD-ROM drivers and the Root Directory. 1.5 1.5 Definition Definition Definition Definition of of Terms Terms For the remainder of this document the following definitions apply: Sector Sector - Is a sector of data on a CD. This is in all cases 800 bytes. Virtual Virtual Virtual Virtual Sector Sector - Is a sector of data on an emulated device. This document only addresses 200 byte device (for emulation) Virtual Virtual Virtual Virtual Disk Disk - A series of sectors on the CD which INT 13 presents to the system as a drive with 200 byte virtual virtual virtual virtual sectors sectors sectors sectors . There are 4 virtual sectors found in each “sector” on a CD

附件2-6：BM可引导光盘格式 2.0 ISO-9660 and the Booting Catalog One goal of this specification is to maintain ISO-9660 compatibility while providing system BIOSs with a simple way of getting to the location on the CD that contains the material to be booted.ISO-9660 defines that a"Primary Volume Descriptor"must reside at sector 10(16 decimal),relative to the start of the session,followed by any number of other Volume Descriptors,followed by a"Volume Descriptor Set Terminator."The El Torito Bootable CD Specification builds on this format by requiring a"Boot Record"Volume Descriptor as defined in section 8.2 of ISO-9660.See figure ora description ofthe Boor Record.This"Boot Record"must reside at sector 11(17 decimal)in the last session on the CD. The Boot Record contains an absolute pointer to the Boot Catalog.The Boot Catalog is a collection of 20 byte entries(as described below),packed 40 entries to the sector.There is no limit to the number of sectors the Boot Catalog uses.This catalog allows the system to pick a proper boot image and then to boot from the selected image.The image may be virtualized into INT 13 drive number 00 or 80 for bootable disk emulation,or n+l for a"non-bootable"emulation,where n is the number of the last hard drive initialized by the BIOS.The image may also simply be some code which will be loaded at boot time(no emulation).The BIOS will choose a drive number between 81 and FF when "no emulation"is specified. There are 5 types of entries diagrammed in figures 2-6.These entries define a validation procedure for the bootable CD,an Initial/Default entry,a section header,a section entry,and a Section Entry Extension. 2.1 Validation Entry This must be the first entry in the boot catalog.The Validation entry validates that a booting catalog is present on the disk and identifies the manufacturer of the CD.If this entry is valid,it is assumed that the rest of the entries are valid.See figure 2 for a description of the Validation Entry. 2.2 Initial/Default Entry The initial entry must contain a boot image which consists of generic programs/drivers that use only the BIOS provided INT 13 interface.The BIOS INT 13 interface consists of functions 0-19 and may optionally include functions 40-48.This entry will always be used by a BIOS that does not use any of the provided section headers.See figure 3 fora description of the Initial/Default Entry. 2.3 Section Header If the CD was created for a machine with a BIOS incorporating this specification,the Section Header precedes a group of entries from which the BIOS may boot the computer.The section header has an identification string.If the BIOS understands the ID,string it may choose to boot the system using one of these entries in place of the INITIAL/DEFAULT entry.A good example would be a BIOS that supports multi-language capability.The BIOS manufacturer defines a header string and selection criteria.When CD's have a section that incorporates the header string and section entries,the BIOS automatically boots software in the native language of the BIOS.See Figure 4for a description ofthe Section Header. 2.4 Section Entry Section Entries must follow a Section Header.The Section Entry looks a lot like the Initial/Default Entry except the unused bytes contain selection criteria.The format of the selection criteria is a function of the BIOS vendor.the other fields are standardized for compatibility reasons.In the case of a foreign language BIOS three bytes would be used to identify the language.If the BIOS does not support languages,the Default entry determines the appropriate language and reinitiates the boot procedure using the proper boot image.If the 13 bytes provided for selection criteria are insufficient,a Section Entry Extension can be added by setting bit 5 of byte 1.See "Section Entry Extension"for details.See Figure5 for a description of the Section Entry. Version 1.0 Copyright 1994 Phoenix Technologies and IBM All Rights Reserved. Page 6

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 6 2.0 2.0 ISO-9660 ISO-9660 ISO-9660 ISO-9660 and and the the Booting Booting Booting Booting Catalog Catalog Catalog Catalog One goal of this specification is to maintain ISO-9660 compatibility while providing system BIOSs with a simple way of getting to the location on the CD that contains the material to be booted. ISO-9660 defines that a “Primary Volume Descriptor” must reside at sector 10 (16 decimal), relative to the start of the session, followed by any number of other Volume Descriptors, followed by a “Volume Descriptor Set Terminator.” The El Torito Bootable CD Specification builds on this format by requiring a “Boot Record” Volume Descriptor as defined in section 8.2 of ISO-9660. See figure 7 for a description of the Boot Record. This “Boot Record” must reside at sector 11 (17 decimal) in the last session on the CD. The Boot Record contains an absolute pointer to the Boot Catalog. The Boot Catalog is a collection of 20 byte entries (as described below), packed 40 entries to the sector. There is no limit to the number of sectors the Boot Catalog uses. This catalog allows the system to pick a proper boot image and then to boot from the selected image. The image may be virtualized into INT 13 drive number 00 or 80 for bootable disk emulation, or n+1 for a “non-bootable” emulation, where n is the number of the last hard drive initialized by the BIOS. The image may also simply be some code which will be loaded at boot time (no emulation). The BIOS will choose a drive number between 81 and FF when “no emulation” is specified. There are 5 types of entries diagrammed in figures 2-6. These entries define a validation procedure for the bootable CD, an Initial/Default entry, a section header, a section entry, and a Section Entry Extension. 2.1 2.1 Validation Validation Validation Validation Entry Entry This must be the first entry in the boot catalog. The Validation entry validates that a booting catalog is present on the disk and identifies the manufacturer of the CD. If this entry is valid, it is assumed that the rest of the entries are valid. See figure 2 for a description of the Validation Entry. 2.2 2.2 Initial/Default Initial/Default Initial/Default Initial/Default Entry Entry The initial entry must contain a boot image which consists of generic programs/drivers that use only the BIOS provided INT 13 interface. The BIOS INT 13 interface consists of functions 0-19 and may optionally include functions 40-48. This entry will always be used by a BIOS that does not use any of the provided section headers. See figure 3 for a description of the Initial/Default Entry. 2.3 2.3 Section Section Section Section Header Header If the CD was created for a machine with a BIOS incorporating this specification, the Section Header precedes a group of entries from which the BIOS may boot the computer. The section header has an identification string. If the BIOS understands the ID, string it may choose to boot the system using one of these entries in place of the INITIAL/DEFAULT entry. A good example would be a BIOS that supports multi-language capability. The BIOS manufacturer defines a header string and selection criteria. When CD’s have a section that incorporates the header string and section entries, the BIOS automatically boots software in the native language of the BIOS. See Figure 4 for a description of the Section Header. 2.4 2.4 Section Section Section Section Entry Entry Section Entries must follow a Section Header. The Section Entry looks a lot like the Initial/Default Entry except the unused bytes contain selection criteria. The format of the selection criteria is a function of the BIOS vendor, the other fields are standardized for compatibility reasons. In the case of a foreign language BIOS three bytes would be used to identify the language. If the BIOS does not support languages, the Default entry determines the appropriate language and reinitiates the boot procedure using the proper boot image. If the 13 bytes provided for selection criteria are insufficient, a Section Entry Extension can be added by setting bit 5 of byte 1. See “Section Entry Extension” for details. See Figure 5 for a description of the Section Entry

附件2-6：IBM可引导光盘格式 Version 1.0 Copyright  1994 Phoenix Technologies and IBM All Rights Reserved. Page 9 Figure 5 - Section Entry Figure 6 - Section Entry Extension Offset Offset Type Type Description Description Description Description 0 Byte Boot Indicator. 88 = Bootable, 00 = Not Bootable 1 Byte Boot media type. This specifies what media the boot image emulates in bits 0-32. Bits 6 and 7 are specific to the type of system. Bits 0-3 count as follows 0 No Emulation 1 1.2 meg diskette 2 1.44 meg diskette 3 2.88 meg diskette 4 Hard Disk (drive 80) 5-F Reserved, invalid at this time bit 4 - Reserved, must be 0 bit 5 - Continuation Entry Follows bit 6 - Image contains an ATAPI driver bit 7 - Image contains SCSI drivers 2-3 Word Load Segment. This is the load segment for the initial boot image. If this value is 0 the system will use the traditional segment of 7C0. If this value is non-zero the system will use the specified segment. This applies to x86 architectures only. For “flat” model architectures (such as Motorola) this is the address divided by 10. 4 Byte System Type. This must be a copy of byte 5 (System Type) from the Partition Table found in the boot image. 5 Byte Unused, must be 0 6-7 Word Sector Count. This is the number of virtual/emulated sectors the system will store at Load Segment during the initial boot procedure. 8-0B D Word Load RBA. This is the start address of the virtual disk. CD’s use Relative/Logical block addressing. 0C Byte Selection criteria type. This defines a vendor unique format for bytes 0D-1F. The following formats have currently been assigned: 0 - No selection criteria 1- Language and Version Information (IBM) 2-FF - Reserved 0D-1F Byte Vendor unique selection criteria. Offset Offset Type Type Description Description Description Description 0 Byte Extension Indicator. Must be 44 1 Byte Bits 1-4 - Unused 5 - 1 = Extension Record follows, 0 = This is final Extension 6-7 - Unused 2-1F Byte Vendor unique selection criteria