This is the first Commodore computer, the PET, or the Personal Electronic Transactor.
It appears that they just made up that description, though, as the name “PET” was apparently chosen to capitalize on the
pet rock fad going on at the time.
Some PETs have a black screen-trim, some are blue. The black-trim PET seen above has a simple adhesive sticker applied for the
large label seen below the screen, but the blue-trim system has a nice painted metal plaque.
Where did the PET come from?
There was an earlier Commodore computer, the KIM-1, but Commodore didn’t design it,
they inherited it when they bought MOS Technologies,
who designed and produced computer chips – the KIM-1 was a way to demonstrate the power of the MOS 6502 CPU to the industrial community.
Chuck Peddle was an engineer at MOS who worked on their 6502 CPU,
as well as the KIM-1 computer. When Commodore wanted a reliable source of chips for their computers, they bought MOS,
renamed it as the Commodore Semiconductor Group, and Chuck Peddle became a full-time Commodore employee.
His first order of business – convince Commodore that calculators were “out”, computers were “in”. It worked – Chuck Peddle
went on to design the PET, one of the very first user-friendly computers. It was designed around the MOS Technologies 6502 CPU,
which eventually came to be used in many of the popular computers of the day –
the Apple II, Atari 400/800, AIM-65, and others.
The PET has a built-in display, although it looks like a monitor perched on top. It is part of the machine
and does not come off. Very stylish and user-friendly.
This is one of the few computers with a built-in cassette drive – very handy, but the keyboard is one of the worst!
The keys are of a type known as ‘chiclet’, tiny and difficult to type on. Touch-typing is impossible.
The PET has four external expansion ports. A parallel port, a cassette recorder port, the system bus,
IEEE-488 port. The IEEE-488 is relatively complex, allowing up to 15 devices on the bus.
Commodore released a giant dual-drive floppy-disk unit which plugged into the IEEE-488 port. You can see it on the
PET 4032 page.
That built-in cassette drive is very convenient, but its origins are less than impressive – it’s merely a modified generic external cassette tape recorder
bolted to the underside of the PET body. Saving money is the name of the game!
Early on, PET users figured-out a way to make the screen update faster,
hence the entire system would run faster. This was accomplished by typing in the
“POKE 59458,62” command sequence from the keyboard.
To test this theory, I ran this short BASIC program on my PET 2001-8:
10 FOR X=1 TO 1000
20 PRINT X;
30 NEXT X
It works! The only obvious side-effect seems to be random ‘twinkling’ on the screen.
[Technical explanation: The PET will not update the video memory (static RAM) while painting the display,
only in between screens. You can trick the system by switching bit 5 of the 6522 VIA I/O Register B from
“input mode” to “output mode” – now the system no longer waits for the video sync signal, thinking that it’s
always present, and updates the screen as fast as it can.
There is a penalty for this, though, as the display will now show random speckles throughout.]
Unfortunately, on later versions of the PET, this POKE command sequence will NOT make the system run faster,
instead it distorts the screen and can eventually damage the circuit.
This became known as the “Killer Poke”, because it might kill your computer.
The requisite PET 2001 “open hood” photo – the top of the PET, normally screwed down, opens for maintenance like the hood of your car.
There’s really not much the owner can do inside of the PET, except increase the RAM from 4K to 8K, if this has not already been done.
The entire body of the PET – the base, the upper section, and the monitor, are all made of sheet metal.
Here you can also see the cassette drive held in-place by brackets and bolts.
This nice ‘blue’ PET has some especially old ROM chips installed – white ceramic! With just a hint of rust…
Most IC chips seen are encased in black plastic – cheaper and more durable. Both of these ceramic chips are cracked.
Want composite video from your PET-2001? Try this circuit from the Commodore Pet Users Club of England!
(Correction: 2200mf = 2200pf)
The PET was quite popular in schools due to its simple use and all-in-one design –
Commodore released numerous PET systems, each slightly different than the other,
but the original 2001 series is the only one with the internal cassette drive and the tiny keyboard.
Easter-egg? – In an early PET Microsoft Basic, type the command WAIT 6502.
The screen will fill with the text “MICROSOFT”. This apparently was inserted by Bill Gates himself in order to assert
Microsoft’s copyright on PET BASIC after he had had an argument with Commodore founder Jack Tramiel. This does NOT work on my PET 2001-8 system,
it requires the newer version of BASIC available on the ‘full-size keyboard’ models.
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