commodore vic 20 design
                      Commodore VIC-20

The Commodore VIC-20 was announced in 1980, roughly three years after Commodore’s first personal computer, the Commodore PET.

The VIC-20 was the first computer of any description to sell one million units. It was described as “one of the first anti-spectatorial, non-esoteric computers by design…no longer relegated to hobbyist/enthusiasts or those with money, the computer Commodore developed was the computer of the future“. The VIC-20 (in Germany, VC-20, in Japan, VIC-1001) is an 8-bit home computer that was sold by Commodore Business Machines.

Early Price :  $299.95 USD (1980)
Today’s Price :  $778.73 USD (2018)

Commodore VIC-20: Overview

Manufacturer :  Commodore Business Machines
Type :  Home computer
Release date :  Year- 1980
Discontinued :  January 1985 (34 years ago)
Display :  Commodore 1701
OS (Operating System) :  Commodore KERNAL / Commodore BASIC 2.0
CPU :  MOS Technology 6502 at 1.108404 MHz (PAL) at 1.02 MHz (NTSC)
Graphics :  VIC (176 x 184) 3-bpp
Memory :  20 KB ROM + 5 KB RAM (expandable to 32 KB), 3.5 KB for BASIC (expandable to 27.5 KB)
Storage :  Cassette tape, floppy disk
Sound :  3 × square, 1 × noise, mono
Input :  Tape, floppy disk, cartridge

Commodore VIC-20: Technical specifications

commodore vic 20 mainboard
                            VIC-20 Mainboard

The VIC-20 shipped with 5 KB RAM, but 1.5 KB of this was used by the system for various things, like the video display (which had a rather unusual 22×23 char/line screen layout), and other dynamic aspects of the ROM-resident BASIC interpreter and KERNAL (a low-level operating system). Thus, only 3583 bytes of BASIC program memory for code and variables was actually available to the user of an unexpanded machine.

Ports And Sockets

The VIC-20 had card edge connectors for program/expansion cartridges and a tape drive (PET-standard Datassette). The VIC-20 did not originally have a disk drive (the VIC-1540 disk drive was released in 1981).

The computer also had a single DE-9 Atari joystick port (compatible with the digital joysticks and paddles used with Atari 2600 videogame consoles), a serial CBM-488 bus (a serial version of the PET’s IEEE-488 bus) for daisy chaining disk drives and printers and a TTL-level “user port” with both RS-232 and Centronics signals (most frequently used as RS-232, for connecting a modem).

software cartridge of commodore vic 20
               Software cartridge

The VIC had a ROM cartridge port to allow for plug-in cartridges with games and other software as well as for adding memory to the machine. Port expander boxes were available from Commodore and other vendors to allow more than one cartridge to be attached at a time. Cartridge software ranged from 4–16 KB in size, although the latter was uncommon due to its cost and only larger software houses produced 16 KB cartridges.

The VIC-20 could be hooked into external electronic circuitry via joystick port (the so-called “user port” or the memory expansion–cartridge port) which exposed various analog to digital, memory bus, and other internal I/O circuits to the experimenter. The BASIC language could then be used (using the PEEK and POKE commands) to perform data acquisition from temperature sensors, control robotic stepper motors, etc.


graphics of commodore vic-20
          16-color capability

The graphics capabilities of the VIC chip (6560/6561) were limited but flexible. At startup the screen showed 176×184 pixels, with a fixed-color border to the edges of the screen. Since a PAL or NTSC screen has a 4:3 width-to-height ratio, each VIC pixel was much wider than it was high. The screen normally showed 22 columns and 23 rows of 8-by-8-pixel characters; it was possible to increase these dimensions up to 27 columns, but the characters would soon run out the sides of the monitor at about 25 columns.

Just as on the PET, two different 256 character sets were included, the uppercase/graphics character set and the upper/lowercase set, and reverse video versions of both. Normally, the VIC-20 was operated in high-resolution mode whereby each character was 8×8 pixels in size and used one color. A lower-resolution multicolor mode could also be used with 4×8 characters and three colors each, but it was not used as often due to its extreme blockiness.

It was possible but difficult to mix graphics with text above or below it, or to have two different background and border colors, or to use more than 200 characters for the pseudo-high-resolution mode. The VIC chip could also process a light pen signal (a light pen input was provided on the DE-9 joystick connector) but few of those ever appeared on the market. 


The VIC chip had three pulse wave sound generators. Each had a range of three octaves, and the generators were located on the scale about an octave apart, giving a total range of about five octaves. In addition, there was a white noise generator. There was only one volume control, and the output was in mono.

Commodore VIC-20: History

japanese language keyboard of commodore vic 20
The VIC-1001 was the Japanese version of the VIC-20. It had Japanese-language characters in the ROM and on the front of the keys.

In April 1980, at a meeting of general managers outside London, Jack Tramiel declared he wanted a low-cost color computer. When most of the GMs argued against it, he said: “The Japanese are coming, so we will become the Japanese.” This was in keeping with Tramiel’s philosophy which was to make “computers for the masses, not the classes”.

The concept was championed at the meeting by Michael Tomczyk, newly hired marketing strategist and assistant to the president, Tony Tokai, General Manager of Commodore-Japan, and Kit Spencer, the UK’s top marketing executive. Then, the project was given to Commodore Japan; an engineering team led by Yash Terakura created the VIC-1001 for the Japanese market. The VIC-20 was marketed in Japan as VIC-1001 before VIC-20 was introduced to the US.

VIC-20s went through several variations in their three and a half years of production. First-year models (1981) had a PET-style keyboard with a blocky font while most VIC-20s made during 1982 had a slightly different keyboard also shared with early C64s. The rainbow logo VIC-20 was introduced in early 1983 and has the newer C64 keyboard with gray function keys and the Revision B motherboard. It has a similar power supply to the C64 PSU, although the amperage is slightly lower.

external storage
The Commodore 1530 C2N-B Datasette provided inexpensive external storage for the VIC-20

A C64 “black brick” PSU is compatible with Revision B VIC-20s; however, the VIC’s PSU is not recommended on a C64 if any external devices such as cartridges or user port accessories are installed as it will overdraw the available power. Older Revision A VIC-20s cannot use a C64 PSU or vice versa as their power requirement is too high.

The VIC-20 was intended to be more economical than the PET computer. It was equipped with 5 KB of static RAM and used the same MOS 6502 CPU as the PET. The VIC-20’s video chip, the MOS Technology VIC, was a general-purpose color video chip designed by Al Charpentier in 1977 and intended for use in inexpensive display terminals and game consoles, but Commodore could not find a market for the chip.

Commodore VIC-20: Reception

Even with some of its limitations, it makes an impressive showing against the Apple II, the Radio Shack TRS-80, and the Atari 800“. The magazine praised the price (“Looking at a picture, it might cause you to think $600 would be a fair price, but it does not cost $600—the VIC 20 retails for $299.95”), keyboard (“the equal of any personal-computer keyboard in both appearance and performance. This is a remarkable achievement, almost unbelievable considering the price of the entire unit”), graphics, documentation, and ease of software development with the KERNAL.




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