VIC-20

    A home computer made by Commodore with a 6502
   CPU, similar in style to the Commodore 64 and Commodore
   C16.  The VIC-20 was released before the C64, and after the
   Commodore PET(?).  It was intended to be more of a low-end
   home computer than the PET.

   The VIC-20 had connectors for game cartridges and a tape
   drive (compatible with a C64).  It came with five kilobytes
   of RAM, but 1.5 KB were used by the system for various
   things, like the video display (which had an unusual 22x20
   char/line screen layout), and other dynamic aspects of the
   operating system (such as it was).  The RAM was expandable
   with a plug-in cartridge which used the same expansion port as
   games.  Port expander boxes were available to allow more than
   one cartridge to be connected at a time.

   RAM cartridges were available in several sizes: 3K, 8K, 16K
   and 32K.  The internal memory map was re-organised with the
   addition of each size cartridge, leading to the situation that
   some programs would only work if the right amount of memory
   was available.  The 32K cartridges were all third-party and
   had switches to allow the RAM to be enabled in sections so
   that any expansion size could be achieved.

   BASIC programs could use at most 24 KB of RAM.  Any extra
   occupied the location usually used by ROM cartridges
   (i.e. games).  This allowed people to copy ROM cartridges to
   tape and distribute them to their friends, who could load the
   tape into the top 8k of their 32k RAM packs.

   The name "VIC" came from the Video Interface Chip that was
   also used in the other, later, Commodore 8-bit computers.

   (2000-03-28)