Date: Wed, 10 Jul 1996 20:22:43 +0200 (MET DST) From: J Wunsch <j@uriah.heep.sax.de> To: freebsd-hackers@freebsd.org (FreeBSD hackers) Cc: jleppek@suw2k.hisd.harris.com (James Leppek) Subject: Re: bootable CD's (fwd) Message-ID: <199607101822.UAA10672@uriah.heep.sax.de> In-Reply-To: <9607101511.AA02412@suw2k.hisd.harris.com> from James Leppek at "Jul 10, 96 11:11:12 am"
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As James Leppek wrote: > If anyone comes up with any pointers I am willing to give it a try, I am > also trying to get the info from gigabyte. What magic do you expect? I don't know, but i would blindly assume that booting the CD will be done in the same way as booting any other device. The BIOS code searches all available devices, and tries to load the very first sector onto address 0:0x7c00. If the loaded sector ends in 0x55aa, it will simply be executed. It's up to the executed code to decide what needs to be done next. That's why you could put a boot-selector MBR there, or you could put the 7.5 KB BSD bootstrap there as well. CD-ROM sectors are 2 KB, not only 512 bytes, but who says you cannot examine the very first 512 bytes only? The most important work that is required is a cdboot subdirectory, initially cloned from biosboot, but with support for a cd9660 file system to load the kernel from. Anyway, you've got full 32 KB of available space on a CD-ROM (there's 0x8000 bytes space in front of the cd9660 header), so this shouldn't be a very big problem. Merging the bootstrap into a cd9660 image could be accomplished by ``dd conv=notrunc'' in the simplest case. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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