1980s Vintage Computers


Commodore PET

PET 2001

The PET has a special place in the history of micro-computers, as it was one of the biggest sellers in the 1979 / 1980 period, when computers were aimed at both the home and business market. Many people instantly recognise the PET as it stood out from the usual 'terminal plus box' computer.

The Commodore PET family started with the 2001 model in 1977 and progressed through to the SuperPET 9000 in 1981. Most of the machines are 6502 based, the SuperPET added a more powerful 6809 as a 2nd processor (allowing full backwards compatibility).

Each model came as a complete system, and the all-in-one design of the early PETs was distinctive and is still instantly recognisable. Common features included:

  • Built in BASIC
  • Cassette port (also a built in cassette on the initial model 2001).
  • Monochrome screen, initially 40 columns x 20 rows, then 80 columns on later models.
  • Edge connectors for an IEEE-488port (used to connect printers and floppy disk drives), a user port and a bus port for a direct connection to the processor.

The name stood for 'Personal Electronic Transactor' .

After the PET came to the end of its life Commodore released the cheaper VIC-20 and Commodore 64 for home use, which were hugely successful. Commodore entered the IBM PC compatible market and also developed the highly successful Amiga range. There was a lot of overlap between these ranges, for example the last PET (8296) was sold until 1986.

I have the following machines in my collection.

Model 2001

This was the first PET model, launched in 1977. It was a popular machine and found many admirers, from educational use, hobbyists, and some business users. The first machines only had 4K of RAM, mine has 8K, but even this was very limiting so several third-party memory expansion boards were available to take the memory up to 32K.  It has a built in system ROM  (6K) and BASIC (8K), and with additional memory could run 6502 assemblers and even compliers. The screen could display upper and lower case letters, and an attractive range of graphics symbols. These features encouraged a large library of software to be written. 

The 2001 model was found to be slow in updating its display, until someone discovered a way of speeding up the graphics routines with a POKE to memory. This was fine, but on later machines the graphics hardware was improved and the same POKE caused the screen to go blank and was know as 'the killer POKE'. 

Here are some of the chips used on the motherboard:

- Main RAM 16 x MOS MPS 6550 (8K)
- Main ROM 7 x MOS MPS 6540 (14K)
- Video RAM 2 x MOS MPS 6550 (1K)

When I first received my machine it displayed random characters on power-up. Following this guidance I bought some more MOS 6550 memory chips and swapped out the faulty ones (about 4). The machine now displays the message

 *** COMMODORE BASIC *** 
7127 BYTES FREE 

but then locks up. I suspect one of the ROMs or some other circuit has failed.

Model 2001-16

This machine was an evolutionary step from the original 2001. The motherboard was redesigned, to use larger memory chips, and the layout was altered so the chips were rotated by 90  (but I don't know why!).  A proper layout keyboard was added, with the option of a business layout, which meant numbers rather than graphics on the top row of keys (the functionality was the same). This is the only PET in my collection that currently is in full working order. The previous owner made some minor modifications (eg added a reset switch to avoid power cycling) and kept it in regular use.

Model 4000

This machine has a 12" green screen, but other wise was very similar to the earlier 2001-16. New versions of BASIC were released, and these were often available as upgrades to earlier machines. My model is currently faulty, it used to display random characters but now displays a blank screen.

Model 8032-SK

This machine was the first PET to feature a detachable keyboard and a monitor with tilt and swivel. My example has been put away and needs to be cleaned before testing.

Commodore PET links

Picture courtesy of Click Here to go to the Old-Computers.com web site


This page was last revised on: 16/06/12