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From: elg@usl (Eric Lee Green)
Newsgroups: comp.arch,comp.unix.wizards,comp.os.misc
Subject: Re: Shared libraries (Was: Re: Big Programs Hurt Performance)
Message-ID: <286@usl>
Date: Sat, 10-Oct-87 18:24:19 EDT
Article-I.D.: usl.286
Posted: Sat Oct 10 18:24:19 1987
Date-Received: Thu, 15-Oct-87 01:39:48 EDT
References: <8714@utzoo.UUCP>
Organization: CACS, Univ of SW La, Lafayette, LA
Lines: 31
Xref: mnetor comp.arch:2630 comp.unix.wizards:4875 comp.os.misc:287

in article <8714@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) says:
> Xref: usl-pc comp.arch:776 comp.unix.wizards:1359 comp.os.misc:161
>> Needless to say, the Amiga OS is not Unix, for one thing, Unix isn't
>> going to run on a 512K machine with no MMU and two floppies...
> You might be interested to know that early versions of Unix ran on machines
> on which 512KB would have been considered an impossible dream, with no MMU,
> and with hard disks not much bigger or faster than modern floppies.  It was
> a bit primitive by modern standards, but it did work.

I assume you are talking about the PDP-11. The PDP-11 does have a MMU,
which does address relocation (i.e. you have a virtual address space
of 64K, located in a larger physical address space of 256K to
4 megabytes depend on 18, 20, or 22 bit models). I've never used a
PDP-11 myself, but I have the architecture manual for the critter
sitting somewhere in my closet... what the world needs is a 32 bit
PDP-11 :-).

I am not certain as to how Minix is implemented on a 68000-based
machine. Probably they use the old pc-relative-relocatable-code trick
of OS9-68K, or use an intelligent relocating loader like the AmigaDOS
loader. Although how you would handle forks is beyond me (all your
pointers in stuff on the heap would be pointing back to the old copy
of the heap, not to the current one that you just generated!).
However, suffice it to say that Minix is not "full" Unix, not even v7
(no swapping, for one thing) and that 68000 machine code is nowhere
near as terse and compact as PDP-11 or even eighty-eighty-sux (8086).

--
Eric Green  elg@usl.CSNET       from BEYOND nowhere:
{ihnp4,cbosgd}!killer!elg,      P.O. Box 92191, Lafayette, LA 70509
{ut-sally,killer}!usl!elg     "there's someone in my head, but it's not me..."