1023 cylinder boot
Newsgroups: comp.unix.sco.misc From: firstname.lastname@example.org (Stephen M. Dunn) Subject: Re: 1023 Cylinder Limit Date: Mon, 14 Feb 2000 03:58:49 GMT Message-ID: <FpwJ21.20C@bokonon.ussinc.com> References: <email@example.com> In article <firstname.lastname@example.org> "Steve Morris" <Stephen.Morris@btinternet.com> writes: $Go to restart and I get the terse error message "CYL OVF". $ $This apparently relates to an old limitation that I was aware of years ago $with regard to the root filesystem having to reside with the first 1023 $cylinders of your hard disk. Since then, it's changed; SCO Unix now uses a separate boot filesystem, so that you don't have to fit the whole root filesystem under the 1024-cylinder limit. But the general idea is the same: you have to fit _something_ within those first 1024 cylinders.
$However, I had thought that by the release of 5.0.5 that this would've been $a thing of the past. Don't blame SCO; they had nothing to do with the design of the BIOS on your system. The problem here is that the standard BIOS calls use a 10-bit quantity to represent the cylinder number, and that means cylinder numbers can only be from 0 to 1023, inclusive. Once you've loaded the Unix kernel and it's running, it uses its own disk drivers, which are not limited to what the BIOS sees, but until that point, you have to use the BIOS calls, which means you're limited to the first 1024 cylinders of the drive. $1. Is there any way around this problem? Your boot filesystem defaults to 20 MB. This, plus a little bit of stuff that comes before it (divvy table, boot loader, etc.), need to reside in the first 1024 cylinders, so you'll need slightly more than 20 MB free there. The rest can follow from cylinders 1024 onwards without problems. $2. How can I determine how many cylinders my SCSI HD has? (Looking at $manufacturers web sites doesn't have this info).
It's not actually how many physical cylinders the hard drive has, but rather how many logical cylinders the host adapter says it has, which will be a different number. Between the hard drive and the host adapter, there are no cylinders, heads, or sectors; there is simply a series of numbered blocks. However, to make this look more like a hard drive, the host adapter maps it into cylinders, heads, and sectors; that way, standard BIOS calls will work. Exactly how this mapping is done varies from one host adapter to another, and there may be host adapter settings that influence it, too. During installation of Unix, it may print a line on the console listing the geometry that the host adapter is presenting. My system has an ATA hard drive, so the line won't look exactly the same, but here are the lines printed for my two hard drives: %disk 0x01F0-0x01F7 14 - type=W0 unit=0 cyls=1025 hds=255 secs=63 %disk 0x0170-0x0177 15 - type=W1 unit=1 cyls=944 hds=14 secs=40 Yours will look close enough that you can recognize them. Failing that, check the documentation for your host adapter. -- Stephen M. Dunn (SD313), CNE, ACE email@example.com ---------------------------------------------------------------------------- Senior Manager United System Solutions Inc. 104 Carnforth Road, Toronto, ON, Canada M4A 2K7 (416) 750-7946 x251
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