If you’ve ever looked at the back and wondered what all the Commodore 64 connectors are for, wonder no more. I’ll explain them to you.
Commodore 64 connectors on the side of the machine
The first connectors you need to know about are on the side, not on the back. Looking at the computer from the front, there are three connectors on the right-hand side: two 9-pin Atari-style controller ports and a round DIN connector for the power supply. Useless trivia: DIN is an acronym for Deutsches Institut für Normung, which translates to “German Institute for Standardization.” Commodore liked to use these types of connectors.
Note that there’s a connector in the back where the power supply will also fit. Plugging it in there will seriously damage the machine. Plug the power supply into the side.
Most single player games use a joystick in the second port, which is the one in the middle. A quirk in the 64’s I/O chips made it easier to program for the second port than the first.
Commodore 64 connectors on the back
Looking at the machine from the back, there are six connectors and a switch.
The connector on the far left is a cartridge port, originally used for game cartridges. As disk drives gained popularity, cartridges became rarer. Disks were cheaper to produce than cartridges, and provided higher capacity. Commodore disk drives were notoriously slow, however, which provided another use. Many companies quickly produced cartridges that sped up the disk drive. Fast load cartridges became a fixture in this port.
Later in the C-64’s lifetime, RAM expansion also plugged into this port. Don’t plug RAM expansion in unless you also have a heavy-duty power supply. You’ll blow the power supply and potentially damage the computer.
The slide switch next to the cartridge port selects whether the 64 will display on channel 3 or channel 4 of a television.
The RCA connector next to the slide switch is an RF output, for connecting to a television’s antenna connector. In the 64’s heyday, this was the only input most televisions had. This is one of two options for connecting a 64 to a TV.
The DIN connector next to the RF switch was an A/V port. Early 64s had a 5-pin port, while later 64s had 8 pins. The 5-pin port provides composite output, audio output, and audio input. The 8-pin port adds separated composite video output, which today we call S-Video.
IEC serial port for disk drives and printers
The DIN connector next to the A/V port is an IEC serial port, a proprietary serial bus for disk drives and printers. It was a simplified and cost-reduced derivative of the industry standard IEEE-488 bus. Commodore used IEEE-488 in the PET, but cost constraints kept it out of the 64, 128, and VIC-20. If you didn’t want to use a Commodore printer, several companies produced interfaces that plugged into the IEC bus and allowed a standard Centronics printer to work.
Note that the power supply will fit into this port, but you will seriously damage your Commodore if you plug it in there. The chip you’ll blow, the 6526 CIA, hasn’t been produced since 1992, so it’s difficult to find today and tends to cost between $20-$25.
The port next to the IEC serial port is for tape drives. In the United States at least, the tape port either went unused, or your printer interface plugged into it to get power. Tape drives were popular in Europe, so in Europe, this port got more work.
The last port is the user port. This was something of a catch-all port, for anything Commodore didn’t put somewhere else. Usually Commodore users plugged a modem in here. Oddly enough, this port was also pretty close to the Centronics standard, so it was possible to connect a printer to this port as well. Most software expected the printer to reside on the IEC bus though, so not many people did this.