Path: utzoo!attcan!uunet!husc6!mailrus!tut.cis.ohio-state.edu!osu-cis!killer!elg
From: elg@killer.UUCP (Eric Green)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga UNIX
Message-ID: <4585@killer.UUCP>
Date: 25 Jun 88 06:10:22 GMT
References: <8806212043.AA00625@cory.Berkeley.EDU>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 33

In message <8806212043.AA00625@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) says:
>>If you wanted to restrict your 68000 system in the same way as the 80x86,
>>to 64K segments, you could allow only register relative code to be used.
>>This would give you a fork that's just as good as any on the 80x86 machines.
>	Which you can do ... make all pointers 16 bit integers and then
>whenever you make a pointer reference offset it by A4 (or whatever).
>But frankly, this would cause more harm than good and be awefully slow!

Actually, using 16-bit relative addressing is FASTER, on a 68000, than
full 32-bit direct addressing. Don't believe me? Go look at the cycle
count in your 68000 assembler manual.

There's a reason the Manx compiler has a "small" model, and that's it.
Manx doesn't extend that paridigm to the heap, however, as an Amiga
Unix would have to do, because of the 32-bit pointers used by Amiga OS
etc.

>	More harm than good, because all those standard Amiga structures
>use normal 32 bit pointers, and one is bound to have a couple of them lying
>around!

If one is implementing a Unix operating system on the Amiga, why in
the world would you want to have a couple of 32-bit pointers to
AmigaDos hanging around?

No, the primary argument is simply that most modern Unix programs will
not fit in a 64K address space, and thus Unix on a 68000 sans MMU
could never be more than a toy.

--
Eric Lee Green    ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg
          Snail Mail P.O. Box 92191 Lafayette, LA 70509              
"Is a dream a lie if it don't come true, or is it something worse?"