Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!haven!mimsy!chris From: chris@mimsy.umd.edu (Chris Torek) Newsgroups: comp.unix.wizards Subject: Re: 4BSD file system structure Message-ID: <20892@mimsy.umd.edu> Date: 23 Nov 89 00:32:06 GMT References: <3410@netcom.UUCP> <20643@mimsy.umd.edu> <1602@minyos.xx.rmit.oz> <20@ocpt.ccur.com> Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742 Lines: 37 In article <20@ocpt.ccur.com> pechter@ocpt.ccur.com (Bill Pechter ) writes: >... there was a boot prom on Vax 11/750's that read in the boot block >from cyl 0, sector 0, track 0 -- but that was the only Vax that did that. Yes, the 750 did this; but it is not the only one. The 8200, for instance, also reads block 0 and jumps to it; and microVAXen with RD-series disks read block zero, but rather than executing the result, they interpret it as a set of additional blocks to read, and other mysterious things. Other computer systems use similar bootstraps. Still others (such as the Power-6/32) do something even weirder: read a Unix file system, open the file `/etc/fstab', and read the first line. (Gak!) As a result of the latter, the 4.3BSD-tahoe distribution for the tahoe includes a `fake' first line in /etc/fstab, that names /dev/xfd0a. The first few lines of /etc/fstab on one of the UCB machines: /dev/xfd0a:/: / ufs xx 1 1 /dev/dk0a / ufs rw 1 1 /dev/dk0b none swap sw 0 0 /dev/dk0b /tmp mfs xx,-s=24000 0 0 /dev/dk8b /tmp ufs rw 1 2 /dev/dk3b /usr ufs rw 1 2 (/tmp exists twice; the `mfs' entry is fake, as yet.) >It was a pretty limited (i.e. AWFUL) way to do things. DEC had to go to >the console tape mode on the 11/750 when they went to Vaxclusters... Actually, it is a fairly reasonable way to boot from a disk, since it does not hard-code anything too terribly (unlike CCI's `assume you have a 4.2BSD file system' scheme). If *everything* is in ROM, it becomes difficult to fix. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@cs.umd.edu Path: uunet!mimsy!chris