附件2-6：BM可引导光盘格式 5.0 CD Boot Procedures This purpose of this section is to describe the intended sequence of events for booting from the various CD formats described above.These procedures should guarantee that software can boot and operate as the software vendor intends. The BIOS provides three INT 13 functions for assigning and deassigning the CD.These functions are documented in the next section and referenced in the paragraphs below. 5.1 Floppy Booting The total capacity of a CD is 600+meg(decimal),give or take a little compression.The purpose of using a floppy emulation is to get the system booted under a specific operating system,load a device driver which understands the true format of the CD,usually ISO-9660,and then put the system back in its normal operating configuration.This sequence of events gives the software on the CD the"normal"configuration of the system and makes the CD available as the same drive letter the user would normally have assigned.Only a small portion of the CD is wasted on the boot image.Another advantage of the floppy image is that you can place several of them on a single CD,each with a customized system configuration.Several entries can be made in the catalog,each with different booting criteria. 5.2 Hard Disk Booting The purpose of booting as a hard disk is to provide a large MS-DOS compatible CD-ROM storage space on which programs may reside and/or access data.This lends itself well to stand alone/protected applications which do not use full system resources.Booting the CD as a hard disk normally requires that all applications on the CD are INT 13/MS-DOS based.The system is not returned to its"normal"operating configuration and software is not intended for installation.This is for applications that run directly from the CD.This does not restrict an application from installing a device driver and using it.In fact,this is encouraged for those applications which require encryption or copy protection.What must be kept in mind is that the CD is a"slow"device,the INT 13 interface can access the data at about the same speed as any driver in this environment. 5.3 No Emulation Booting When the Media Type is set to zero the BIOS does not use the CD to emulate a disk.The boot operation loads the requested number of sectors directly to the specified segment.When loading is complete the BIOS will jump to segment:0. The associated piece of software can be a"loader"(which provides its own CD interface),or it can be a stand alone program.The El Torito specification allows for the loading of FFFF sectors(This would allow the BIOS to fill the entire low 640k memory area with data).Once the system jumps to segment:0,the program can retrieve its boot information by issuing INT 13,Function 4B,AL=01.After the boot process has been initiated the INT 13 Extensions(functions 41-48) will access the CD using 800 byte sectors and the LBA address provided to INT 13 is an absolute sector number.This gives any program running in no emulation mode the ability to locate the boot catalog,and any other information on the CD,without providing a device driver. 5.4 System Optimization The Default/Initial Catalog Entry may contain a floppy image which can examine the system and/or query the user about his system configuration,select a proper Section Entry,and then reboot the system using this Section Entry.This program on its first invocation may write configuration information to the users Hard Disk and then not question the user on subsequent booting operations.This is particularly useful when a CD has multiple uses or the user purchases several CD's from the same software vendor.The selection program will already have configuration information available. Version 1.0 Copyright 1994 Phoenix Technologies and IBM All Rights Reserved. Page 13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 13 5.0 5.0 CD CD Boot Boot Procedures Procedures Procedures Procedures This purpose of this section is to describe the intended sequence of events for booting from the various CD formats described above. These procedures should guarantee that software can boot and operate as the software vendor intends. The BIOS provides three INT 13 functions for assigning and deassigning the CD. These functions are documented in the next section and referenced in the paragraphs below. 5.1 5.1 Floppy Floppy Booting Booting Booting Booting The total capacity of a CD is 600+ meg (decimal), give or take a little compression. The purpose of using a floppy emulation is to get the system booted under a specific operating system, load a device driver which understands the true format of the CD, usually ISO-9660, and then put the system back in its normal operating configuration. This sequence of events gives the software on the CD the “normal” configuration of the system and makes the CD available as the same drive letter the user would normally have assigned. Only a small portion of the CD is wasted on the boot image. Another advantage of the floppy image is that you can place several of them on a single CD, each with a customized system configuration. Several entries can be made in the catalog, each with different booting criteria. 5.2 5.2 Hard Hard Disk Disk Booting Booting Booting Booting The purpose of booting as a hard disk is to provide a large MS-DOS compatible CD-ROM storage space on which programs may reside and/or access data. This lends itself well to stand alone/protected applications which do not use full system resources. Booting the CD as a hard disk normally requires that all applications on the CD are INT 13/MS-DOS based. The system is not returned to its “normal” operating configuration and software is not intended for installation. This is for applications that run directly from the CD. This does not restrict an application from installing a device driver and using it. In fact, this is encouraged for those applications which require encryption or copy protection. What must be kept in mind is that the CD is a “slow” device, the INT 13 interface can access the data at about the same speed as any driver in this environment. 5.3 5.3 No No Emulation Emulation Emulation Emulation Booting Booting Booting Booting When the Media Type is set to zero the BIOS does not use the CD to emulate a disk. The boot operation loads the requested number of sectors directly to the specified segment. When loading is complete the BIOS will jump to segment:0. The associated piece of software can be a “loader” (which provides its own CD interface), or it can be a stand alone program. The El Torito specification allows for the loading of FFFF sectors (This would allow the BIOS to fill the entire low 640k memory area with data). Once the system jumps to segment:0, the program can retrieve its boot information by issuing INT 13, Function 4B, AL=01. After the boot process has been initiated the INT 13 Extensions (functions 41-48) will access the CD using 800 byte sectors and the LBA address provided to INT 13 is an absolute sector number. This gives any program running in no emulation mode the ability to locate the boot catalog, and any other information on the CD, without providing a device driver. 5.4 5.4 System System Optimization Optimization Optimization Optimization The Default/Initial Catalog Entry may contain a floppy image which can examine the system and/or query the user about his system configuration, select a proper Section Entry, and then reboot the system using this Section Entry. This program on its first invocation may write configuration information to the users Hard Disk and then not question the user on subsequent booting operations. This is particularly useful when a CD has multiple uses or the user purchases several CD’s from the same software vendor. The selection program will already have configuration information available