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From: kdarling@hobbes.catt.ncsu.edu (Kevin Darling)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: 8-bit death
Message-ID: <1991May3.220043.28760@ncsu.edu>
Date: 3 May 91 22:00:43 GMT
References: <1991Apr30.112820.2451@sugar.hackercorp.com> <1991May1.064455.3058@kessner.denver.co.us> <21135@cbmvax.commodore.com> <1991May3.041705.9907@kessner.denver.co.us> <21216@cbmvax.commodore.com>
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In <21216@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:
> [...]
> How about an OS like the original Mac OS, or OS/K, which work with 68000s,
> but being base register addressed, have 32K limits to code or data chunks. 

Small correction: OS9/68K (OSK) _itself_ has no limits; it works with 32-bit
addresses, and any size chunk.  The base 68000 cpu offset-limit handling is
something the PIC/reentrant applications take care of themselves, via jump
tables or using a temporary register for far offsets.

And the "limit" there is 64K, not 32K... since the available 68000 register
addressing offsets are +/-32K, y'see.  OSK compilers automatically offset
data references by $8000.  Options deal with the more remote data/code.

> Are these 8, 16, or 32 bit operating systems?  All three numbers apply,
> depending on where you look.  These processors have a 32 bit programming
> model, but the OS has addressing limits reminisent of a bank-switched 8 bit
> OS, while the actual ALU and data bus on the CPU hardware is 16 bits wide.

Hey, blame _Motorola_ for the 64K offset limits on a 68000 <g>.  "Pure"
(reentrant) code for the Amiga OS has the same data offset limitations.

I must say that too many Amiga programmers shy away from the reentrant and
position-independent modes of the 680x0, btw.  Treating a 68K cpu like a
giant 6502 makes me want to throw up :-).  The fact that those addressing
modes are _faster_ than the long addressing modes often used instead, is
taking a long time to sink in.  Yet they're what the cpu was designed for!
To me, the Ami relocating loader is more Intel-like, than Motorola-like.

Full agreement with the rest of your message, tho.  Keep up the good work.
This the first time I've ever found even a _tiny_ reason to contradict ya!
  deep regards - kevin <kdarling@catt.ncsu.edu>