Bootable CD-ROM Format Specification

6.0 New INT 13 Functions

Transparent system operation is not always desirable because software installation usually requires the system to be in

its “normal” configuration. For this reason 3 new INT 13 functions are provided. These functions allow the system to

return to its normal state or to enter the “boot” state a second time after the boot process has already been initiated.

6.1 INT 13 Function 4A - Initiate Disk Emulation

This function takes a pointer to the Specification Packet and uses it to make the specified drive letter available, using

the Image LBA “pointer” in the supplied packet.

Registers at call:

AH = 4A

AL = 00

DS:SI - Specification Packet as defined in figure 9

Registers on return

AX - Return Codes

CF - Clear if selected drive is emulating

CF - Set if system not in emulation mode

6.2 INT 13 Function 4B - Terminate Disk Emulation

This function returns the system to a configuration that matches a normal floppy or hard disk boot. If the CD booted

as a floppy, the “A” drive returns and the CD becomes driver addressed. If the CD booted as a hard disk, the drive

numbers are all decremented by 1, this returns all hard disks to their standard/normal device numbers.

Registers at call:

AH = 4B

AL = 00, Return Status and Terminate Emulation

AL = 01, Return Status only, Do Not Terminate Emulation

DL = Drive number to terminate, 7F = Terminate all

DS:SI - Empty Specification Packet, See figure 9

Registers on return:

DS:SI - Completed Specification Packet, See Figure 9

AX - Return Codes

CF - Clear if system released

CF - Set if system not in emulation mode