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T13/2132-D Revision 3 June 23, 2010
22 Working Draft Enhanced Disk Drive - 4 (EDD-4)
that is on the floppy or hard disk drive (HDD) shall be packed four sectors of data to each sector on the CD or
DVD. This packing shall be performed in a linear fashion so that floppy or HDD sectors zero through three
become the first sector in the image on the CD or DVD. Packing shall continue so that floppy or HDD sectors
four through seven are the second sector on the CD or DVD, floppy or HDD sectors 8 through 11 are the third
sector in the image on the CD or DVD. This process is repeated until all the data is on the CD or DVD. INT 13h
FNs 00h through 3Fh shall then unpack the data based on the calling parameters. This method allows software
on the CD or DVD to use the system BIOS without taking into account the CD or DVD hardware or sector size.
This method also allows a floppy or HDD image to be tested and debugged using a normal floppy or HDD. Once
the image on the media is booting and operating properly, the image may then be transferred to the CD or DVD
with a high degree of confidence that it will function properly.
INT 13h Functions 41h through 49h access the CD or DVD using non-emulated sector LBA's in the native sector
size of the CD or DVD. INT 13h FN 48h shall return the total number of 2KB sectors on the CD or DVD and shall
set the flag that indicates the geometry is invalid. This capability allows software to use generic ISO-9660 or
other file system drivers without requiring a CD or DVD hardware specific driver. This capability allows the
software to boot and run, provided the software uses INT 13h functions exclusively, regardless of the interface
bus type. This means that a CD or DVD boot image may be constructed that works the same on ATAPI, Fibre
Channel, SCSI, USB, 1394, and other buses. If the system is EDD-3 compliant, the Initial/Default Image may
make an INT 13h FN 48h call, determine the interface bus type, and then boot an image with native CD or DVD
drivers to perform the requested operation.
7.2.3 No Emulation Boot
If an image is marked as No Emulation Boot, the system BIOS shall load the specified number of sectors and
jump to the specified segment number to start the boot program executing. Since this is a no emulation boot, the
system BIOS shall not provide access to the media through INT 13h FNs 00h through 3Fh. The system BIOS
shall assign the CD-ROM drive a device number. A common industry number is A0h. This is outside the range
of normal BIOS hard drive numbers (above 9Ah), but still within INT 13h range limitation.
7.2.4 Floppy Boot
When the system attempts to boot a Floppy based image, it shall assign device number 0 to the image. If there
are one or more standard floppy drives present in the system, they shall be sequentially numbered by the BIOS
starting from one and increasing.
EDD-4 supports 3 different floppy formats: 1.2MB, 1.44MB, and 2.88MB. All of these formats can be created on
a floppy disk first, tested, and then transferred to the target CD or DVD. Table 14 describes the geometries INT
13h FN 8h shall return for each floppy type.
The total capacity of a CD is more than 600MB. Many floppy images may be embedded on one CD or DVD,
since floppy images shall be 2.88MB or less. One reason for making a bootable floppy image is to boot the
system, load a CD or DVD specific device driver and then provide access to all the media. This capability allows
a simple OS, such as DOS, to be used for accessing a self-contained CD. One application for this capability is
system recovery or system restore.
7.2.5 Hard Drive Boot
When the system attempts to boot a Hard Disk Drive (HDD) based image, it shall assign device number 80h to
the image. If there are one or more standard disk devices present in the system, they shall be numbered
sequentially starting at 81h and increasing.
The geometry returned by INT 13h FN 08h is based on the partition table embedded in the first sector of the HDD
image. The partition type of HDD images shall include cylinder-head-sector (CHS) addresses. Any partition type
Table 14 — Floppy Geometries
Type Cylinders Heads Sectors
1.2MB 80 2 15
1.44MB 80 2 18
2.88MB 80 2 36