Date: Wed, 19 Nov 1997 18:22:39 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: tony@dell.com (Tony Overfield) Cc: tlambert@primenet.com, hackers@FreeBSD.ORG Subject: Re: >64MB Message-ID: <199711191822.LAA14282@usr05.primenet.com> In-Reply-To: <3.0.3.32.19971118043753.0071582c@bugs.us.dell.com> from "Tony Overfield" at Nov 18, 97 04:37:53 am
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> >1) You can't trust a *user process* to call the BIOS (it's not > > the sword that's the problem, it's what the peasent *does* > > with the sword that makes us make them illegal for everyone > > but the knights and the king). > > I didn't realize the bootloader had user processes. This is in the general sense of a callable VM86() interface. This assumes the kernel is up. > >2) The BIOS INT 13 code has a 2G limit on partition size, unless > > you can guarantee all the devices in your machine support > > LBA mode (even then the limit on LBA is lower than the limit > > in FreeBSD... 64bits >> 32 bits). > > This appears to be completely wrong. > > First, I'm talking about bootloaders. I assume you agree that the > bootloader should use INT 13. > > Second, the INT 13 interface (without LBA mode) is limited > to 8.4 GB, not 2 GB. A DOS partition (assuming we use the DOS MBR and aren't idiots, we are tied to the DOS partition table) is limited to C/H/S values. You have tha ability to map an 8G space with four descriptors. > Third, the limit for LBA INT 13 is 64-bits worth of sectors, or > 2^73 bytes. This should last us for several more years. The LBA limit is irrelevant. It's not usable, so it might as well be fiction. > >3) Gate A20 (now you will argue that Dell hardware doesn't use > > BIOS code that expects a wrap in memory). > > Of course I will! I doubt any BIOS has ever been made that needs > it. You'll no doubt cite some heap-o-crud(tm), obsolete system made > by some long defunct company, probably with some ironic name like > "Leading Edge" or something.... ;-) Yep. Right where I was going... Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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