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June 23, 2010
7.3.4 Initial/Default Entry
Every boot catalog shall have an Initial/Default entry. This entry contains the starting address of the initial boot
image. The default entry is started if the system BIOS does not have the capability to boot from other boot
images in the boot catalog. Normally, a system BIOS does not check for additional boot images. If there are
multiple boot image possibilities, the Initial/Default entry may be a program that has the appropriate selection
mechanism for choosing the proper boot image. See Table 8 for a description of the Initial/Default Entry.
Offset
Type
00h
Byte
01h
Byte
02-03h
Word
04h
Byte
05h
Byte
06h-07h
Word
08h-0Bh
DWord
0Ch-1Fh
Byte
7.3.5 Section Header
If the CD or DVD has boot images in addition to the Initial/Default image, pointers to the images are grouped into
sections. The identification string in the section header shall be used to determine if the image pointers in that
section point to bootable images. If the BIOS is not setup to use a specific section as identified by the ID string,
then the section shall be ignored. A good example of a section would be to identify a specific language for the
Working Draft Enhanced Disk Drive - 4 (EDD-4)
Table 17 — Initial/Default Entry
88h - Header ID indicates a bootable image is present. 00h indicates that a
non-bootable image is present
Boot media type. The boot image shall fall into one of three categories: Floppy,
Hard Drive, or None.
ID Description
0 No Emulation
1 1.2MB diskette
2 1.44MB diskette
3 2.88MB diskette
4 Hard Drive
05h-FFh Reserved
Load Segment. This shall be the segment address where the first emulated sector
of data is loaded into system memory. If this field cleared to zero, the default value
of 07C0h shall be used. For flat memory model architectures (such as Motorola),
this is the memory address divided by 10h.
System type. This shall be a copy of byte 5 (system type) from the partition table
found in the boot image.
Reserved
Sector Count. This shall be the number of emulated sectors the system shall
transfer from the CD to the Load Segment address in system memory during the
boot process. This field will normally be set to 01h for 80x86 systems that are
booting a floppy or hard drive image. For No Emulation Booting, this field could
potentially ask for 32MB of data to be loaded from the CD or DVD before jumping
to the boot address.
Load Block. This shall be the absolute start sector on the CD or DVD of the image
to be used in the emulation.
Reserved
Description
T13/2132-D Revision 3
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