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B

BillW50

The BBC Master computer (6502-based, or it might have been 6512) had the
ability to use a "second processor"; IIRR more than one type was
available, but certainly 80186 was one of them. It sort of - IIRR - used
the existing computer as a sort of terminal to the new one. The 80186
came with something - I think it was a version of DR DOS - which created
a (somewhat crippled, as it loaded from floppies) decidedly bizarre sort
of PC.

Wow that is very interesting. I know tons about the MOS 6502 and 8510,
but absolutely nothing about the 6512. And how did that second processor
work?

For example the Commodore 128 used MOS 8510 and a Z80 soldered right on
the motherboard. But the Z80 did not do anything as far as I know until
you ran CP/M. Then the 8510 handled the hardware while the Z80 handled
the OS and the applications.

Everything sounds wonderful and all. But there was one huge
disadvantage. And I think this applies to all dual processors back then.
As they shared the same address and data lines. Thus one had to be put
to sleep before the other one woke up and the reverse is true too. So
all of this waking and putting to sleep slowed things down more than
just using one processor alone.

Although the huge advantage was that it was more compatible with far
more things than one processor alone. The Commodore 128 for example when
it first came out bragged that it could run more software than anything
before it. And I think that was true for a few years after. But it
wasn't MS-DOS compatible and MS-DOS applications was growing far faster
and it had overtaken even the C128 a bit later.

So was this the same with the BBC Master computer?
 
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B

BillW50

My memory, which stinks, is that we went from 8086 to 80286.
Somewhere I think I remember someone designing an a
custom (not a computer) board about an 80186.

Yes most everybody went from 8086 to the 80286. I do remember that the
80186/88 just wasn't a big hit. And I think it might have been Intel's
own fault. As I don't remember a lot of time between the two and why use
the 80186/88 when the 80286 was so much better? But then the 80386 (aka
386) killed off the 80286, then the 486, etc.
 
B

BillW50

In J. P. Gilliver (John) typed:
BillW50 <[email protected]> said:
On 5/18/2012 9:13 PM, Todd wrote: []
My memory, which stinks, is that we went from 8086 to 80286.
Somewhere I think I remember someone designing an a
custom (not a computer) board about an 80186.

Yes most everybody went from 8086 to the 80286. I do remember that
the 80186/88 just wasn't a big hit. And I think it might have been
Intel's own fault. As I don't remember a lot of time between the two
and why use the 80186/88 when the 80286 was so much better? But then
the 80386 (aka 386) killed off the 80286, then the 486, etc.
I think the '186 was a bit of a fork in the design: popular with
standalone and embedded system designers, I think it had extra things
on-chip (controllers? ports? I can't remember), which even the '286
(though that was more powerful as a processor), and possibly even '386
and '486 and later, didn't.

I can remember even less about the 80188: I do remember that around
that time there were variations that were 16 bit internally but 8 bit
externally (might have been 32/16, but I think it was 16/8) - in other
words, used an 8 bit bus outside the chip to keep the pin count and
thus package size down - and I _think_ the '186/'188 might have been
something to do with that. I'm more certain that the 8086/8088
difference was connected with such a concept.

Ah yes. some of it is coming back. Many thanks.
 
B

BillW50

In J. P. Gilliver (John) typed:
BillW50 <[email protected]> said:
On 5/18/2012 8:38 PM, J. P. Gilliver (John) wrote: []
The BBC Master computer (6502-based, or it might have been 6512)
had the ability to use a "second processor"; IIRR more than one
type was available, but certainly 80186 was one of them. It sort of
- IIRR - used the existing computer as a sort of terminal to the
new one. The 80186 came with something - I think it was a version
of DR DOS - which created a (somewhat crippled, as it loaded from
floppies) decidedly bizarre sort of PC.

Wow that is very interesting. I know tons about the MOS 6502 and
8510, but absolutely nothing about the 6512. And how did that second
processor work?

I too know nothing of the 6512 - could just be my imagination. The
original BBC microcomputer was definitely 6502; I just wasn't sure if
the Master was the same one.

I can't remember much of how the second processor worked: googling for
"bbc master second processor"
(with the quotes, i. e. as a phrase) comes up with 6 results, the
first of which tells me that the Master used the 65C02 (and the
original the 6502A) - I had _thought_ it was different in some way!
The first 5 of the 6, though not very informative about it, are all
interesting reading - http://chexum.co.uk/pics.php?aid=1 being just
lots of pictures of old (mostly pre-PC) computers (including
Colossus, but lots of Spectrum/Commodore/Amstrad etc. as well).
[]
Everything sounds wonderful and all. But there was one huge
disadvantage. And I think this applies to all dual processors back
then. As they shared the same address and data lines. Thus one had to
be put to sleep before the other one woke up and the reverse is true
too. So all of this waking and putting to sleep slowed things down
more than just using one processor alone.

I _think_ the BBC series' second processor units were more or less
complete computers in themselves, with their own RAM, and were just
_controlled_ by the original computer (possibly via ports?) - though
obviously did have to share video circuitry at least.
[]
So was this the same with the BBC Master computer?
Sorry, can't remember: maybe some here will. (Some of the above hits
suggest that even the previous model - the model B - could have the
second processor fitted.)

Ah very interesting and many thanks.
 
B

BillW50

In David H. Lipman typed:
NEC V20 = 8088
NEC V30 = 8086

It does have the 80186 superset of instructions and if I remember
correctly you can set a flag for a 8080 mode and run CP/M.

Ah thanks! My Sharp PC4501 laptop from '88 ran with a V20. It was XT
compatible, but supported 1MB of RAM. And supposedly you could run some
programs that were 286 only. But I don't recall the exact details.
 
D

David H. Lipman

From: "BillW50 said:
In David H. Lipman typed:

Ah thanks! My Sharp PC4501 laptop from '88 ran with a V20. It was XT
compatible, but supported 1MB of RAM. And supposedly you could run some
programs that were 286 only. But I don't recall the exact details.

There is no such thing as 286 programs.

What the 286 brought to the table was a 24bit addressesable memory which gave it ~16MB as
compared to the 20bit adddressable memory of the 8088/86 which was only 1MB.

With the 8088/86 you could only add RAM using the Expanded Memory Module specification and
software had to be compliant to recognize this external memory.

With the 80286 you could have up to 16MB using the Extended Memory Module specification
and thaus Extended Memory Managers such as QEMM was borrne as well as Windows 286.

The 80386sx also used the 24bit addressesable memory scheme top be backward compatible to
80286 support chip-sets. That is why a 80386sx module could be inserted into a 286 socket
which gave a computer 32bit operation but only 16MB. This was on contrast to a full 386
CPU which has a 32bit processor and 32bit addressesable memory.

Each CPU back then needed its own complementary match coprocessor 8086 - 8087, 80186 -
80187, 80286 - 80287 and 80386/386sx - 80387/387sx.

There were two instances where a CPU was made for older hardware compatipbility. The 8088
and the 386sx.

The 8088 was created as a 16bit processor but with an 8bit bus such that older 8080/85
8bit support hardware could be used as it was widely available.

The 80386sx was created as a 132bit processor but with an 16bit bus such that older 80286
16bit support hardware could be used as it was widely available.

The 80486 combined the 80386 and 80387 into one chip with a small cache.

The 80486sx was a stupid idea and I won't go into that.

At this time Intel realized that you can not copyright a number. Thus the "Pentium" chip
was born but was really just a more advanced version of the 80486 schema and was the 5th
generation Intel CPU. AMD had the 80586 CPU.
 
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B

BillW50

There is no such thing as 286 programs.

Huh? Protected Mode software ran under the 80286 and not under 8086.
Lots of examples, like OS/2 v1, DOS 286, and so on. And one of the huge
disadvantages of the 80286 running in Protected Mode is that it couldn't
switch back to Real Mode without a hardware-initiated reset.
 
B

BillW50

In David H. Lipman typed:
Operating Systems are not "programs." Programs run underneath an
Operting System. Programs inherit what the Operating System provides.

Not only was there protected mode OS, but protected mode applications
too. As once you switched the 80286 to protected mode, it was never
designed to switch back to real mode once again during that session. And
you couldn't run virtually all real mode applications and you were
basically stuck running only protected mode (aka 286) applications.
Although 286 applications did have some benefits like access up to 16MB
of memory and a bug in an application couldn't often crash the OS like a
real mode application could.
 
C

Char Jackson

In message <[email protected]>, David H.

I think you'll find that an OS is a program - a sequence of instructions
obeyed by the processor(s). This particular program may allow other
programs to run (not always the case: the OS program in your car's ECU,
or your washing machine, for example, doesn't. Yet, anyway!).

Hell, even the BIOS is a program!

Oh, where would we be without semantics. :)
 
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