Editing VIC-20 (section)

=== Peripherals and expansion ===
[[File:Commovc20side5580-01 (retuschiert).jpg|thumb|The side of the computer showing the joystick "control port"]]

The VIC-20 has card [[edge connector]]s for program/expansion cartridges and a PET-standard [[Commodore Datasette|Datassette]] tape drive. The VIC-20 did not originally have a disk drive; the [[VIC-1540]] disk drive was released in 1981.

There is one [[Atari joystick port]], compatible with the digital [[joystick]]s and [[paddle (game controller)|paddles]] used with [[Atari 2600|Atari VCS]] and [[Atari 8-bit computers]];<ref name="flynn198206">{{cite news | url=http://www.atarimagazines.com/compute/issue25/035_1_USING_ATARI_JOYSTICKS_WITH_YOUR_VIC.php | title=Using Atari Joysticks With Your VIC | work=Compute! | date=June 1982 | access-date=6 October 2013 | author=Flynn, Christopher J. | pages=79}}</ref> a serial [[Commodore bus|CBM-488]] bus (a serial version of the PET's [[IEEE-488]] bus) for [[daisy chain (electrical engineering)|daisy chain]]ing [[Commodore 1540|disk drives]] and printers; a [[transistor-transistor logic|TTL]]-level "user port" with both [[RS-232]] and [[Centronics]] signals (most frequently used as RS-232, for connecting a [[modem]]<ref>The Commodore VICModem and later models connected directly to the user port's edge connector. But in order to connect the VIC to industry-standard [[modem]]s and other [[RS-232]] devices, the user needed to purchase a separate [[transistor-transistor logic|TTL]]-to-RS232 [[volt]]age converter box (standard TTL voltages lie between 0 and 5&nbsp;V, while RS-232 uses ±12&nbsp;V).</ref>).

The VIC has a [[ROM cartridge]] port for games and other software as well as for adding memory to the machine. Port expander boxes from Commodore and other vendors allow more than one cartridge to be attached at a time. Cartridge size ranges from {{nowrap|4–16 KB}} in size, although the latter was uncommon due to its cost.

The VIC-20 can be hooked into external electronic circuitry via the joystick port, the "user port," or the memory expansion cartridge port, which exposes various analog to digital, memory bus, and other internal [[input/output|I/O]] circuits to the experimenter. [[PEEK and POKE]] commands from BASIC can be used to perform [[data acquisition]] from temperature sensors, control robotic [[stepper motor]]s, etc.
In 1981, Tomczyk contracted with an outside engineering group to develop a direct-connect modem-on-a-cartridge (the [[Commodore 64 peripherals#Serial communications|VICModem]]), which at US$99 became the first modem priced under US$100. The VICModem was also the first modem to sell over 1 million units. VICModem was packaged with US$197.50 worth of free telecomputing services from [[The Source (online service)|The Source]], [[CompuServe]], and [[Dow Jones & Company|Dow Jones]]. Tomczyk also created a [[Special interest group|SIG]] called the Commodore Information Network to enable users to exchange information and take some of the pressure off of Customer Support inquiries, which were straining Commodore's lean organization. In 1982, this network accounted for the largest traffic on CompuServe.{{Citation needed|date=March 2008}}

Commodore's VIC-1010 Expansion allows the user to connect multiple devices to the VIC-20's cartridge port. It has its own power supply and six slots that can be used to connect memory extensions, game cartridges or other peripherals.<ref>{{ citation | url=https://northhertsmuseum.org/north-hertfordshire-museum/collections/object-details/330668/ | title=VIC-1010 Expansion Board | date=11 July 2014 | access-date=5 February 2024 }}</ref>
[[File:VIC-1010-Expantion module.jpg|alt=Commodore VIC-1010 Expansion module|thumb|Commodore VIC-1010 Expansion module]]