When the Media Type is set to zero the BIOS does not use the CD to emulate
a disk. The boot operation loads the requested number of sectors directly
to the specified segment. When loading is complete the BIOS will jump to
segment:0. The associated piece of software can be a "loader" (which
provides its own CD interface), or it can be a stand alone program. The
El Torito specification allows for the loading of FFFF sectors (This would
allow the BIOS to fill the entire low 640k memory area with data). Once
the system jumps to segment:0, the program can retrieve its boot
information by issuing INT 13, Function 4B, AL=01. After the boot process
has been initiated the INT 13 Extensions (functions 41-48) will access the
CD using 800 byte sectors and the LBA address provided to INT 13 is an
absolute sector number. This gives any program running in no emulation
mode the ability to locate the boot catalog, and any other information on
the CD, without providing a device driver.
This sounds really interesting! The big question is how many systems
actually faithfully implement this part of the El Torito spec. Sorry
for being paranoid, but the reality is that if it's not used commonly,
there is an all-too-unfortunately high probability that some cheasy
Taiwan-special (or even made in America) hardware won't support it
correctly. <Insert standard grumbling about the cheap-sh*t Wintel
hardware industry.>
Unfortunately, the only way I know for sure to check would be to make
some ISO images available and ask people to test it and see whether it
works.
* I sent this to eric@andante.jic.com, the author of mkisofs. Bounced.
FYI, Eric Youngdale's new e-mail address (caused by his switching
ISP's) is eric@andante.org.
- Ted
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/