UEFI 2.3.1
12.3.2.1 ISO-9660 and El Torito
IS0-9660 is the industry standard low level format used on CD-ROM and DVD-ROM.
The CD- ROM format is completely described by the “El Torito” Bootable CD-ROM
Format Specification Version 1.0. To boot from a CD-ROM or DVD-ROM in the boot
services environment, an EFI System partition is stored in a “no emulation”
mode as defined by the “El Torito” specification. A Platform ID of 0xEF
indicates an EFI System Partition. The Platform ID is in either the Section
Header Entry or the Validation Entry of the Booting Catalog as defined by the
“El Torito” specification. EFI differs from “El Torito” “no emulation” mode in
that it does not load the “no emulation” image into memory and jump to it. EFI
interprets the “no emulation” image as an EFI system partition. EFI interprets
the Sector Count in the Initial/Default Entry or the Section Header Entry to be
the size of the EFI system partition. If the value of Sector Count is set to 0
or 1, EFI will assume the system partition consumes the space from the
beginning of the “no emulation” image to the end of the CD-ROM.
DVD-ROM images formatted as required by the UDF 2.0 specification (OSTA
Universal Disk Format Specification, Revision 2.0) can be booted by EFI. EFI
supports booting from an ISO-9660 file system that conforms to the “El Torito”
Bootable CD-ROM Format Specification on a DVD- ROM. A DVD-ROM that contains an
ISO-9660 file system is defined as a “UDF Bridge” disk. Booting from CD-ROM and
DVD-ROM is accomplished using the same methods.
Since the EFI file system definition does not use the same Initial/Default
entry as a legacy CD-ROM it is possible to boot personal computers using an EFI
CD-ROM or DVD-ROM. The inclusion of boot code for personal computers is
optional and not required by EFI.
Andrew Fish
On Oct 24, 2012, at 9:27 PM, Ramesh Raju wrote:
> Hi,
>
> if (SectorCount < 2) {
> //
> // When the SectorCount < 2, set the Partition as the whole CD.
> //
> if (VolSpaceSize > (Media->LastBlock + 1)) {
> CdDev.PartitionSize = (UINT32)(Media->LastBlock - Catalog->Boot.Lba
> + 1);
> } else {
> CdDev.PartitionSize = (UINT32)(VolSpaceSize - Catalog->Boot.Lba);
> }
>
> The specification --“El Torito”Bootable CD-ROM Format Specification Version
> 1.0, gives the meaning of "Sector Count" as illustrated below,
> I don't understand why it's different between the case when Sectors < 2 and
> the case when Sectors >=2 ??
>
> <image001.jpg>
>
> Any idea which spec says about partition size is depend on SectorCount values?
>
> Thanks,
> Ramesh
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