Messages in this thread | | | Date | Sat, 28 Aug 1999 14:02:43 -0400 | From | "Theodore Y. Ts'o" <> | Subject | Re: Little-known features of El Torito Spec |
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Date: Sun, 29 Aug 1999 08:07:57 +0930 (CST) From: <dan@shearer.org>
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
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