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June 23, 2010 T13/2132-D Revision 3
Working Draft Enhanced Disk Drive - 4 (EDD-4) 23
that supports CHS is acceptable (e.g., FAT-16 or FAT-32) The partition table shall only have one partition
defined.
7.3 CD/DVD Format
7.3.1 Overview
The system BIOS can boot from a CD or DVD only if the format of the media has been predefined. ISO-9660 is
a basic CD-ROM file system that has been incorporated into current CD and DVD file system standards.
CD/DVD boot uses ISO 9660 as a framework to provide boot capability. ISO 9660 requires that a set of volume
descriptors reside on the media starting at sector 10h. For data CD's, there will usually be a "Primary Volume
Descriptor" at sector 10h followed by a "Set Terminator" at sector 11h. The "Primary Volume Descriptor"
provides a pointer to the directory structures. ISO 9660 has also defined a "Boot Volume Descriptor" (BVD).
BIOSes check the BVS to determine if a CD or DVD id bootable. A CD or DVD shall have a BVS at sector 11h on
the media. The "Set Terminator" shall reside at sector 12h or higher. ISO 9660 requires that a "Set Terminator"
be present. ISO 9660 formatting need not be present for a CD or DVD to be bootable. The only requirement is
that a BVS be present at sector 11h.
7.3.2 Boot Volume Descriptor (BVD)
ISO 9660 does not define the payload for its BVD. This standard provides the necessary formatting to enable
bootability. The BIOS shall check the data in the BVD to determine if boot is possible. Table 15 describes the
BVD format.
Table 15 — Boot Volume Descriptor
Offset Type Description
00h Byte Boot Record Indicator: this field shall be set to 00h
01h-05h Byte ISO-9660 specification identifier: this field shall be set to 43h 44h 30h 30h 31h
("CD001")
06h Byte Descriptor Version: this field shall be set to 01h
07h-26h Byte This field shall be set to: 45h 4Ch 20h 54h 4Fh 52h 49h 54h 4Fh 20h 53h 50h 45h
43h 49h 46h 49h 43h 41h 45h 49h 4Fh 4Eh 00h, 00h, 00h, 00h, 00h, 00h, 00h, 00h,
00h ("EL TORITO SPECIFICATION" padded to the right with zeros).
27h-46h Byte Reserved
47h-4Ah DWord Absolute pointer to the first sector of the boot catalog
4Bh-7FFh Byte Reserved