In the 1970s, Texas Instruments was the main supplier of CPUs for use in calculators. Many companies sold calculator designs based on their chip sets, including Commodore. However, in 1975 TI increased the price to the point where the chip set alone cost more than what TI sold their entire calculators for, and the industry they had built up was frozen out of the market.
Commodore responded by looking for a chip set of their own they could purchase outright, and quickly found MOS Technology, Inc. who were bringing their 6502 microprocessor design to market. Along with the company came Chuck Peddle's KIM-1 design, a small computer kit based on the 6502. At Commodore, Peddle convinced Jack Tramiel that calculators were a dead-end. Instead they should focus on making a "real" machine out of the KIM-1, and selling that for much higher profits. Tramiel demanded that Peddle, and Tramiel's son, Leonard, create a computer in time for the June 1977 Consumer Electronics Show, and gave them six months to do it.
The result was the first all-in-one home computer, the PET. The first model was the PET 2001, including either 4 KB (the 2001-4) or 8 KB (2001-8) of 8-bit RAM. It was essentially a single-board computer with discrete logic driving a small built-in monochrome monitor with 40×25 character graphics. The machine also included a built-in Datassette for data storage located on the front of the case, which left little room for the keyboard. The 2001 was announced at the '77 Winter CES in January 1977 and the first 100 units were shipped in mid October 1977. However they remained back-ordered for months, and to ease deliveries they eventually cancelled the 4 kB version early the next year.
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 non-click motion. Internally a newer and simpler motherboard was used, along with an upgrade in memory to 8, 16, or 32 KB, known as the 2001-N-8, 2001-N-16 or 2001-N-32, respectively.
Sales of the newer machines was 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. Like the 2001-N-8, the 3008 was quickly dropped.
This was essentially the later model 2000 series, but with a larger black-and-green monitor and a newer version of Commodore's BASIC programming language.
By this point Commodore had noticed that many customers were buying the "low memory" versions of the machines and installing their own RAM chips, so the 4008 and 4016 had the sockets punched out of the motherboard.
The 4032 was a huge success in schools, where its tough all-metal construction and all-in-one design made it better able to stand up to the rigors of classroom use. Just as important in this role was the PET's otherwise underutilized IEEE 488 port. Used wisely, the port could be used as a simple local area network and allowed printers and disk drives (then very expensive) to be shared among all of the machines in the classroom.
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. Later the upgrade was installed from the factory, creating the 8096.
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. It also included a terminal program which allowed the machine to be used as a "smart terminal" as well, so this single machine could replace many of the boxes currently in use at the university. Additionally this machine became a remote development environment where the user could later upload their creation to a mainframe after completing development and testing on the SuperPET.
Commodore tried to update the PET line with a new redesign called the CBM-II series (also known as the B series). These were not as successful and were ultimately abandoned. However, due to demand, the original PET machines were revived and the CBM-II case style was retained. These were known as the SK's (due to the separated keyboard). They also had a swivel monitor. Originally, standard 8032 boards were retrofitted into these cases. Later the SK models got a new mainboard that already included the 64 kB extension directly on the board and were sold as 8296 or, with a built-in 8250 dual disk drive, as 8296-D.
Although not officially a member of the PET series, in 1983 Commodore packaged C64 motherboards in PET 4000-series cases to create the Educator 64. This was an attempt to retake some of the education market they had largely lost by then to the Apple II.
Bitmapping and colors aside, the main limitation of the PET's graphics capabilities was that the character set was "hardwired" in ROM. On many of the PET range's home computer rivals, the look-up address of the character graphics could be changed and pointed to RAM, where new characters could be drawn by a programmer to create custom graphics shapes. From a programming point of view, this was a relatively simple method of producing good-looking graphics images, and because of this, as well as the acceptable speed obtainable by a BASIC program moving character objects on the screen compared to bitmap graphics, many programs with a certain amount of graphics, including a fair amount of games, were made this way even on bitmap-capable machines. The PET's lack of the character set remapping feature must therefore be said to constitute a major weakness in the machine's design.
Somewhat offsetting this drawback, the PET's ROM-restricted character set—an ASCII-1963 deviation known as PETSCII—was one of the most varied and flexible of the era, allowing PET games with rudimentary graphics to be created, exemplified by clones of video games such as Space Invaders. Also, the many popular text adventure games of the time, some multiplatform, some created for the PET line, did not need graphics at all. For specialized applications, alternative character sets could be programmed into an EPROM inserted in the character set ROM socket. Alternative character set EPROMs with diacritics and mathematical symbols were available in the aftermarket.