Editing Commodore PET (section)

===Graphics display===
[[Image:Tentoonstelling mens en computer Weeknummer, 79-13 - Open Beelden - 22208.ogv|thumb|thumbtime=12|Dutch newsreel from 1979 in which a PET is shown]]

In the home computer market, the PET line was soon outsold by machines that supported high-resolution color graphics and sound, mainly the [[Apple II]] (which shipped in June 1977), [[Atari 8-bit computers|Atari 400/800]] (1979), and, in particular, Commodore's own bestselling [[VIC-20]] (1980/81). Commodore released a ''High Resolution Graphic'' board for the PET using the [[Thomson EF936x]] graphics chip with a resolution of 512×512 pixels.<ref>{{cite web |url=http://www.cbmhardware.de/cbmwiki/index.php/PET-Grafikkarte_Commodore_ASSY_No._324402-01_für_CBM_8296 |title=PET-Grafikkarte Commodore ASSY No. 324402-01 für CBM 8296 |publisher=CBMPET.DE |access-date=2010-03-30 |archive-url=https://web.archive.org/web/20110911232829/http://www.cbmhardware.de/cbmwiki/index.php/PET-Grafikkarte_Commodore_ASSY_No._324402-01_f%C3%BCr_CBM_8296 |archive-date=2011-09-11 |url-status=dead }}</ref> In addition, the Apple II, [[TRS-80|TRS-80 Model I]], and Atari 400 (via 3rd party expansions)/800 could all be expanded to a maximum of 48&nbsp;KB of RAM while the PET was limited to 32&nbsp;KB.

Without the ''High Resolution Graphic'' board, the PET's graphics capabilities were limited to a [[character set]] [[Hardwired control|hardwired]] in [[read-only memory|ROM]], similar to the Apple II in text mode. On many of the PET range's home computer rivals, the look-up address of the character graphics could be changed and pointed to [[random-access memory|RAM]], where new characters could be defined 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, which used negligibly more RAM than a standard character display, and significantly less RAM than bitmap graphics. The PET's lack of a remappable character set is a major weakness in the machine's design.

Somewhat offsetting this drawback, the PET's ROM-restricted character set{{snd}} an ASCII-1963 deviation known as [[PETSCII]]{{snd}} was one of the most varied and flexible of the era. It allowed PET games with rudimentary graphics to be created, exemplified by clones of video games such as ''[[Space Invaders]]'' and ''[[Lunar Lander (1979 video game)|Lunar Lander]]''. The PETSCII character set was even flexible enough to allow for the creation of simple [[3D computer graphics|3D]] games such as ''Labyrinth''. This flexibility was achieved by the use of two switchable character sets, allowing the choice of either mixed-case characters, or uppercase with graphics; either could also be displayed as a reverse field, negative image. For specialized applications, alternative character sets could be programmed into an [[EPROM]] inserted in the character set ROM socket. Alternative character set EPROMs with [[diacritic]]s and [[mathematical symbols]] were available in the aftermarket. A 2001-8B model with katakana keyboard and character set was sold in Japan.

In 2012, Commodore enthusiast Steve Gray began a project to convert the Commodore PET to colour.<ref>{{cite web |last1=Gray |first1=Steve |title=The Colour PET Project |url=http://www.6502.org/users/sjgray/projects/colourpet/ |website=6502.org |publisher=Steve Gray |access-date=10 May 2022}}</ref> This involves upgrading a 4032 machine or downgrading an 8032 machine. The result is 16 colours for foreground and background, The colour RAM is located at $8800 which is not used in regular PET machines. Colour PET emulation is available in the newer versions of the Vice Emulator software.

[[File:Kana keyboard.jpg|thumb|Commodore Pet Katakana Keyboard]]

Other than a [[PC speaker]]-class beeper, PETs did not have sound hardware (except for the 8000 models), but it was possible to rig a circuit (attributed to [[Hal Chamberlin]]{{r|progpet|p=289}}) up to the 6522 "user" port that could be used to output square wave tones to an external amplifier, and some games supported this feature.

The PET had two empty sockets on the motherboard for adding expansion ROMs, which could be a total of 8K in size. A predecessor to the cartridge slots on later Commodore machines, they allowed various software add-ons such as machine language monitors. In addition, it was common for commercial programs to include a [[copy protection]] ROM that had to be installed prior to running the application; something of an inconvenience to users owning multiple applications protected in this way, as the chips would have to be swapped in order to run their respective programs.