Bootable CD-ROM Format Specification

Offset Type Description

0 Byte Boot Indicator. 88 = Bootable, 00 = Not Bootable

1 Byte Boot media type. This specifies what media the boot image is intended to

emulate in bits 0-3 as follows, bits 4-7 are reserved and must be 0.

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

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-1F Byte Unused, must be 0.

Figure 3 - Initial/Default Entry

Offset Type Description

0 Byte Header Indicator as follows:

90 -Header, more headers follow

91 - Final Header

1 Byte Platform ID:

0 = 80x86

1=Power PC

2=Mac

2-3 Word Number of section entries following this header

4-1F Character ID string. This identifies a section. This string will be checked by BIOS and

BOOT software. If the string matches, the section should be scanned for boot

images.

Figure 4 - Section Header Entry