The Commodore PET (Personal Electronic Transactor) was a home/personal computer produced from 1977 by Commodore International. A top-seller in the Canadian and United States educational markets, it was Commodore's first full-featured computer, and formed the basis for their 8-bit product line, including the Commodore 64.

The first model of was the PET 2001. Its 6502 processor controlled the screen, keyboard, cassette machines and any peripherals connected to one of the computer's several expansion ports. The PET 2001 included either 4 KB or 8 KB of 8-bit RAM, and was essentially a single-board computer with discrete logic, driving a small built-in monochrome monitor with 40×25 character graphics.

The PET 2001 was announced at the Winter CES in January 1977 and the first 100 units were shipped later that year in October. However, the PET was back-ordered for months and to ease deliveries, early in 1978 Commodore decided to cancel the 4 kB version.

Although the machine was fairly successful, there were frequent complaints about the tiny calculator-like keyboard, often referred to as a "chiclet" keyboard because the keys resembled the popular gum candy. This was addressed in upgraded "dash N" and "dash B" versions of the 2001, which put the cassette outside the case, and included a much larger keyboard with a full stroke motion. Internally a newer motherboard was used, along with an upgrade from static RAM to dynamic RAM and 8, 16, or 32 KB, known as the 2001-8N, 2001-16N or 2001-32N, respectively.

Sales of the newer machines were strong, and Commodore then introduced the models to Europe. However, there was already a machine called PET for sale in Europe from the huge Dutch Philips company, and the name had to be changed. The result was the CBM 3000 series ("CBM" standing for Commodore Business Machines), which included the 3008, 3016 and 3032 models.

Two more machines were released in the PET series. The CBM 8000 included a new display chip which drove an 80×25 character screen, but this resulted in a number of software incompatibilities with programs designed for the 40 column screen, and it appears to have been unpopular as a result. The machine shipped with 32 kB standard as the 8032, but allowed another 64 kB to be added externally.

The last in the series was the SP9000, known as the SuperPET or MicroMainframe. This machine was designed at the University of Waterloo for teaching programming. In addition to the basic CBM 8000 hardware, the 9000 added a second CPU in the form of the Motorola 6809, more RAM memory and included a number of programming languages including BASIC in ROM for the 6502 and APL, COBOL, FORTRAN, Pascal and a 6809 assembler on floppies for the 6809.

Source: Wikipedia, "Commodore PET", available under the CC-BY-SA License.