Date: Tue, 4 Jun 1996 18:01:55 +0200 (MET DST) From: grog@lemis.de (Greg Lehey) To: rhh@ct.picker.com Cc: hackers@freebsd.org (FreeBSD Hackers), questions@freebsd.org (FreeBSD Questions) Subject: Re: LBA and Large IDE driver with 2.1R Message-ID: <199606041601.SAA13540@allegro.lemis.de> In-Reply-To: <199606040154.VAA09475@elmer.picker.com> from "Randall Hopper" at Jun 3, 96 09:54:36 pm
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Randall Hopper writes: > > JULIAN Elischer: >> The slice can be > 512 MB if it is not the BOOTING slice/partition >>> >>> I have FreeBSD 2.1.0-STABLE running fine on a 1.6 Gig disk, and all of >>> the FreeBSD slice lives up on the high 815 meg of the disk. I'm running >>> LBA on an Asus P55TP4XE (dual IDE onboard), and using OS/BS Beta to boot >>> this FreeBSD slice and all the others on this WD31600 as well as my WD31200 >>> on wd0. I have had 0 problems -- FreeBSD seems to pick up the translated >>> geometry and life is good. > > I don't believe that this describes my system. My root, user, and > swap are all above 512Mb (in the single FreeBSD slice I mentioned). The > only thing below 512Mb that's involved here is my boot loader (OS/BS) which > is on wd0 in cylinder 0. My understanding is that the boot loader just > loads up the boot sector in the FreeBSD slice and executes it, and FreeBSD > then uses the BIOS (the LBA is through my BIOS) to load the kernel. > FreeBSD is somehow picking up and using the translated LBA geometry of my > drive OK, because the kernel loads and the OS runs without a hitch (been > running great for months). > > Does the 512MB limit come from the 1024 cylinder limit? If so this > may help explain things. My true cylinder count = 3148. Cylinder count w/ > LBA = 787. If the 512MB is just a derived limit and the 1024 cyl is what > counts, this makes sense. FreeBSD uses the BIOS to load the kernel, my LBA > is through my BIOS, so to the BIOS it's loading below cylinder 1024. The 504 MB (not 512 MB) limit comes from the combination of a number of things. Most older BIOSes have a limit of 1024 cylinders, 16 heads and 63 sectors, which is enough to address 504 MB. It looks as if increasingly BIOSes are coming on the market which have raised these limits. This seems to be the case with your BIOS, which explains why you can boot at all. I'd guess it gives you 64 "heads". Greg
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