Connectors

• a serial bus (a serial version of the Commodore PET's IEEE-488 bus) for daisy-chaining disk drives and printers - 6-pin round DIN.
• a "user port" - a TTL-level port providing 8-bit programmable I/O RS-232 and Centronics signals, e.g. for serial modems - 12-pin male edge connector.
• a single joystick port on the right-hand side, fully compatible with Atari game console joysticks and with C64 joysticks - 9-pin DB9 plug.
• a cartridge slot for memory expansion or software cartridges - 48-pin female edge connector.
• a monitor/RF modulator output socket (both audio and video) - 5-pin round DIN.
• a cassette port - 12-pin male edge connector.
• a power supply socket - 7-pin round DIN (9V) which is powered by a regulated 9V DC power supply (the same as the C64). NOTE: Older VIC-20s use a 2-pin power socket - this requires a 9v AC connection, not DC.

Technical Facts

• It came with 5K of RAM, but 1.5K of this was reserved by the system for use with things such as video display and dynamic aspects of the ROM-resident BASIC interpreter and kernel (low level OS).
• The RAM was expandable using plug-in cartridges, and Commodore released Port Expander boxes that allowed more than one cartridge to be fitted at the same time. Commodore RAM cartridges were available in 3K, 8K or 16K, with or without a BASIC ROM extension. Later, third-parties released 32K RAM expansion cartridges. Whenever a RAM cartridge was installed, the VIC-20's internal memory map was reorganised to cater for the expansion. This meant often that programs were incompatible unless a very specific amount of RAM was detected.
• BASIC programs running on a fully expanded VIC-20 could access at most 24K of RAM. Any extra would occupy memory space used by ROM cartridges, for example games and other commercial software.
• Graphically, the VIC-20 could display up to 128x128 pixels resolution with the unexpanded 5K of RAM. When expanded to 8K or more, it could display up to 192x200. There was actually a further 1K on the board (on top of the 5K) used as video RAM for the VIC chip.
• the VIC chip (aka MOS 5651 in PAL-B form) was followed by the VIC-II in the C64 and the VIC-III in the unfinished C64DX/C65 prototypes, although sound generation was taken out in these two later versions with the new SID chip. The VIC chip would actually get rather hot (as did the VIC-II and TED chips of other CBM machines), and Commodore used several techniques at trying to keep it cool, including thermal paste and metal latches.
• The standard 'text' mode displayed 22x23, although with a few tricks, it could display up to 29x35.
• There were many storage options on the VIC-20 - a Commodore VC-1530 "Datasette" (model code C2N), a serial floppy disk drive such as the CBM 1540 or CBM 1541 both of which stored up to 170K per disk, other floppy drives usable via the IEEE-488 interface, and later on, 3.5" floppy drives such as the CBM 1581, which stored 800K per disk.
• The VIC-20 is for the most part, compatible with all Commodore 64 peripherals.
• The default screen resolution provided by the VIC-1 chip is 22x23 text characters, or 176x184 graphics pixels. However, with an NTSC VIC-1 (the 6560), it can actually support (by removing all borders) 24x29 text characters or 192x232 pixels. The VIC-1 also supports a virtual screen which can be "panned" so the physical screen becomes a "window" into the virtual screen. The maximum scrollable virtual screen on NTSC is 28x32 text chars, or 224x256 pixels.
• The one key capability of the VIC that makes full screen hi-res graphics possible is that it can be made to have each character cell use up 8x16 pixels instead of the standard 8x8 pixel character cell (without this hi-res graphics would only fill half the screen).

Component details reproduced with friendly permission from Sothius' Home, www.sothius.com (shame you closed your site, Sothius, it was great! Ed)

Trivia

• In 1983, in an effort to make the VIC-20 more of a professional machine, Commodore had already begun developing a new 40-column capable VIC chip (to be marketed as the VIC-40), the MOS 6562 - remember the standard VIC chip can only support 22 columns. However, development ceased when the VIC-30 project (soon to be known as the C64) began, with it's VIC-II chip.
  Unlike the PET, Commodore never produced BASIC 4.0 upgrade ROMs for the VIC-20.
  
• The VIC-20 was codenamed 'Vixen' during development, and 'MicroPET' when first shown to the public, because its final name had not been thought of at that time.
• The VIC-20 required an external RF modulator (part number CBM1001027-03 for PAL machines) to run with a standard TV.
• The cassette connector on the VIC was the same as that taken off the Commodore PET, called the "Datassette".
• When the VIC-20 was being prepared for its first public appearance at the CES in 1980, not one but two prototypes were developed: Bob Yannes had hacked together a minimal working prototype using spare PET/CBM parts. The second prototype, brought to the show by Bill Seiler and John Feagans (who was also the mastermind behind the Commodore kernel) had been put together after some preliminary discussions with Bob Yannes.
• Commodore computers prior to the VIC-20 all used the IEEE bus to connect to peripherals such as disk drives and printers. The supply of cables for these became very scarce as there was only one supplier of them, Belden Cables. Because this put Commodore in a difficult position, Jack Tramiel decreed that for future CBM computers, they would "get off that bus! Make it a cable that anyone can manufacture.". And so, starting with the VIC-20, the serial bus was born. It was designed to be just as fast as the IEEE-488 that it replaced.
• The VIC-20 was named after the VIC-1 chip (which provides the VIC-20 with its graphics capability). The "20" is the amount of RAM rounded down (~22K). Michael Tomczyk, who got stuck with the job of deciding on the name, did the rounding. In Germany, the VIC-20 is called the VC-20 because the pronunciation of VIC in German is a naughty word!
• The Commodore C2N cassette recorder actually records two copies of a program onto the cassette, so even if there is an error with the first load, it records it into main memory and the second load is then used to verify against the first in memory.
• The official colour of the VIC-20 case is called "Ivory". The regular typewriter keys are in "Chocolate Brown", and the function keys are in "Mustard" !