On 26/10/2011 08:38, dennis@home wrote:


"John Rumm" wrote in message
o.uk...
On 25/10/2011 23:36, dennis@home wrote:


"Tim Streater" wrote in message
...
In article om,
"dennis@home" wrote:

"Tim Streater" wrote in message
...
In article m,
"dennis@home" wrote:

"Steve Firth" wrote in message
-september.


org
...
"dennis@home" wrote:
[snip]
If only Apple had allowed the clones to build Macs back in the
80s

yes we would still be stuck with an OS that didn't even do
virtual memory.
Windows did that for years before macOS.

No that's bull****. It would have been accurate had you said
that Windows
had protected memory before MacOS.

Well that's not surprising.. it wasn't until the 68030 series came
out that there was a working MMU to run the protection and
coincidently support paging and VM.
That is true for Motorola CPUs as used by Apple.

Mmmm no (again). The 030 was the first in the 68k line to have an
*on-board* MMU. You could perfectly well use a 68020 and use the
68851 MMU as a co-processor with it.

Which MacOS used one of those?

The later versions of classic MacOS, with virtual memory, would
certainly have run on an 020 Mac with MMU.

Anyway they didn't work very well.

Do you mean the 020? (Used in the TGV and Eurofighter according to
WinkyPedia). Or the MMU.

Well its pretty obvious from what I wrote.
maybe your MMU is also defunked?


Having written a tiny OS for the 68000 (see
http://www.clothears.org.uk) I can state that it's a much better
processor than the 8086 ever was. Just a shame that the 68008 wasn't
out in time for IBM to use in the original PC instead of the 8088.

AFAICS there wasn't much in it.
I wrote in 8086 assembler for the 8086 board I designed.
It wasn't any more difficult than assembler for the 68000.

You are having a laugh...

Segmented architecture, 16 bit registers and not many off them, loads
of hard coded use cases for various registers, weak stack handling,
lame edge sensitive interrupt controllers and prioritisation.

All of which still worked if you knew how to use them.

Don't think anyone was claiming they did not work, just that they were
very poor in comparison. Great if you like painting the hall through the
letterbox, but not a way to get a job done effectively.

(you only need look at the dominance of 68K in the embedded market at
the time, to see what people opted for when unconstrained by a need to
be "compatible")

compared with flat memory, 32 registers, orthogonal design etc

No interrupt controllers for the 68000 (at least not when I was

Given it had the ability to deal with three prioritised level sensitive
interrupts without even needing an external controller, this was a very
good thing. With a controller it was far more flexible than the 8086
interrupt system, and without requiring anything like the hideous
complexity introduced by the 8259 and its multitude of obscure modes of
operation.

designing 8086 stuff, it was early as they hadn't even done the 8088
then, the PC hadn't been invented either).
BTW the 8086 instructions were no worse than the 68000, you could do
most things without resorting to the short instructions.

I think your memory must be failing. While it is unrealistic to separate
the instruction set from the architecture anyway (and its that which
makes the 8086 such a dogs breakfast) the instruction sets are not even
comparable. The 68K set allows the programmer to concentrate on
designing code to do the required job, whereas with 8086 you have to
spend fair amount of effort just picking the right registers to use so
you don't have to wast time swapping stuff about when you realise you
need to do a multiply and AX and DX are holding something else, or you
want a loop and happen to have something in CX etc.

The 80186 board I designed was programmed using PL/M and used RMX86.

It was much easier.

Than what? PL/M was better than Intel assembler granted (especially if
you had to use Intel's DOS based tools which were bug city). '186
cleared away a few peripheral chips and was favoured by hardware guys
who could not work out how to do address decoding logic that worked,
but the performance was poor in comparison to 68K.

However it was cheap and made quite a nice controller for an X25
communications board.

They are ok, and indeed I have used them many times (GEC at the time had
a habit of designing intel based embedded systems long after the world
had decamped to motorola). However for any form of comms work the 68302
gives you all the 186 has in terms of embedded peripherals, and
facilities for reducing hardware complexity external to the processor
(chip select and wait state generation etc), but it is in a different
class altogether with a proper three channel communications processor
built in which can transparently handle anything from looking like a bog
standard serial link, to HDLC and various other protocols.


--
Cheers,

John.

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