C64 hardware

The Commodore 64 computer is a lower cost machine intended for personal use. In the United States, the greatest competitors were the Atari 8-bit 400, the Atari 800, and the Apple II. The Atari 400 and 800 had been designed to accommodate previously stringent FCC emissions requirements and so were expensive to manufacture. Though similar in specifications, the two computers represented differing design philosophies; as an open architecture system, upgrade capability for the Apple II was granted by internal expansion slots, whereas the Commodore 64 ‘s comparatively closed architecture had only a single external ROM cartridge port for bus expansion.

  • MOS 6502 CPU
  • 64KB RAM
  • VIC-II graphics chip
  • Cartridge slot
  • $135 bill of materials
  • $595 MSRP at launch

The Commodore 64 performs a RAM test on power up and if a RAM error is detected, the amount of free BASIC memory will be lower than the normal 38911 figure. If the faulty chip is in lower memory, then an ?OUT OF MEMORY IN 0 error is displayed rather than the usual BASIC startup banner. The color RAM at $D800 uses a separate 2114 SRAM chip and is gated directly to the VIC-II.

The graphics chip, VIC-II, features 16 colors, eight hardware sprites per scanline (enabling up to 112 sprites per PAL screen), scrolling capabilities, and two bitmap graphics modes.

The Commodore 64 cartridges map into assigned ranges in the CPU’s address space and the most common cartridge auto starting requires the presence of a special string at $8000 which contains “CBM80” followed by the address where program execution begins. The cartridge can also even map out the BASIC ROM if needed.

Around 300 different cartridges were released for the Commodore 64 , mostly in the machine’s first 2½ years on the market, after which most software outgrew the 16KB cartridge limit.

The Commodore 64 was generally connected to a television but many used a color monitor which did not need an RF modulator. The Commodore 64 supports a tape cassette for saving programs and games etc. Generally the shorter thicker tapes work better and keeping the head clean is also important.

The block diagram shows the design of the Commodore 64 is fairly basic. Some support chips are needed for supporting the serial ports etc.