Text 5475, 95 rader
Skriven 2010-03-02 10:56:31 av Michiel van der Vlist (2:280/5555)
   Kommentar till text 5438 av Bo Simonsen (2:236/100.0)
Ärende: Windows Update Fix
==========================
Hello Bo,

On Monday March 01 2010 19:16, you wrote to me:

 MvdV>> But it wasn't on that PDP8 that I learned programming. That
 MvdV>> didn't happen until a few years later when I worked as a medical
 MvdV>> physicist in the Tijgerberg Hospital in Cape Town.

 BS> Must have been an interesting time, observing the beginning of
 BS> computing on computers.

Indeed, I have lived in interesting times. Saw the first computers, saw the
first man walk on the moon, witnessed the birth of quark and inflation
theories, etc, etc. All very interesting.

Regarding computers: what I find frustrating is that at one time, some 20 years
ago, I had full control over my computers. I could find every bit and have them
switch things on and off trimmed to the microsecond.

Now they have become too complicated to be fully understood by one man. I have
little idea what goes on behind the screens and have no control over it any
more. That is frustrating...

 MvdV>> I got "saddled" with a French minicomputer. An Intertechnique
 MvdV>> Multi 8. It had 12K core memory, a teletype with paper tape
 MvdV>> reader and punch. An optical tape reader, a magnetic tape unit, a
 MvdV>> plotter and an interface to some linear particle detector.

 BS> More advanced with the magnetic tape unit.. I guess it was 8-bit since
 BS> it was called 8?

Yes, it was 8 bit.

It was actually a microcoded processor. The instruction set presented on the
assembler level was not the bottom level. Below it was yet another level of
microcode. A very limited set of instructions that were stored in a diode
matrix that formed the micro programme that defined the instruction set.

In theory it was possible to rewrite (and rewire) the microprogramme to change
the macro instruction set.

As it was the macro instruction set was basically 8 bit, Its addressing space
was 8 bit, but it provided for dealing with variable length registers of 1, 2,
3 or 4 bytes.

Another interesting thing was that because of the magnetic core memory, one did
not have to reload after a shut down. The content of memory was preserved. So
when properly shut down (manually or by the power fail interrupt), once power
came up, it would just carry one where it was shut down without having to
reload anything.


 MvdV>> With it came an interpreter for a BASIC like language, but to
 MvdV>> access the peripherals like the plotter, the tape unit and the
 MvdV>> particle detector, it had to be programmed in assembler.

 MvdV>> And so I learned assembler...

 BS> I guess the BASIC language was a special dialect?

It wasn't BASIV, just BASIC like. IIRC the name was LEM. Langue Elemantaire
Mathematique.

 BS> The problem with assembler is that when you learn it on one machine it
 BS> may not be the same on another one (on another architecture/processor
 BS> to be more precise)

Each processor has its own instruction set and hence its own assembler
language. But instruction sets have many sets in common, so if you have
mastered one, it is not hard to learn another. I think I have programmed in
assembler for a dozen or so processors. Of the top of my head:

SC/MP
6502
6800
6802
6803
6805
6809
6811
68000
8080
80186
80286
Z80

It has been over a decade since I last fired up my universal cross assembler,
so it would take a while to pick it up again. It is not like swimming, one DOES
forget...


Cheers, Michiel

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