Bootable CD-ROM Format Specification

When the boot image is a hard disk, all drives numbered 80 and above are incremented by 1, becoming 81 and up,

and, the CD will become drive 80. This allows software vendors to create stand-alone CD’s that normally run under

MS-DOS and use the standard INT 13 interface to place their software on the CD without regard to the media. The

system’s hard drive remains accessible because the stand alone CD may need some temporary disk storage.

When the boot image is simply a “loader” or stand alone program, and NO EMULATION is desired, the drive

numbers will be unaffected after the boot image is loaded. The specified number of sectors are loaded at the specified

segment (usually 7C0), and then the BIOS jumps to the load address. The software can retrieve a pointer to its boot

information by issuing INT 13, Function 4B, AL=1.

If the Boot Indicator in Byte 0 is not an 88, the system accesses the next boot device, and the CD will now become the

last drive in the user’s drive sequence regardless of the image type. This allows software vendors to distribute data

CD’s which do not require device drivers for MS-DOS style accessing.

4.4 Boot Entry Selection

If the CD has several boot entries, a default entry which boots a selection program may be provided as the

Default/Initial catalog entry. This image will usually be a floppy image which loads a program that selects the proper

boot image by examining the system configuration or questioning the user.