The Commodore 1530 (C2N) Datasette, later also Datassette (a portmanteau of data and cassette), is Commodore‘s dedicated magnetic tape data storage device. Using compact cassettes as the storage medium, it provides inexpensive storage to Commodore’s 8-bithome/personal computers, notably the PET, VIC-20, and C64. A physically similar model, Commodore 1531, was made for the Commodore 16 and Plus/4 series computers.
Typical compact cassette interfaces of the late 1970s use a small controller in the computer to convert digital data to and from analog tones. The interface is then connected to the cassette deck using normal sound wiring like RCA jacks or 3.5mm phone jacks. This sort of system was used on the Apple II and TRS-80 Color Computer, as well as many S-100 bus systems, and allow them to be used with any cassette player with suitable connections.
In the Datasette, instead of writing two tones to tape to indicate bits, patterns of square waves are used, including a parity bit. Programs are written twice to tape for error correction; if an error is detected when reading the first recording, the computer corrects it with data from the second. The Datasette has built-in analog-to-digital converters and audio filters to convert the computer’s digital data into analog sound and vice versa. Connection to the computer is done via a proprietary edge connector (Commodore 1530) or mini-DIN connector (1531). The absence of recordable audio signals on this interface makes the Datasette and clones the only cassette recorders usable with Commodore computers, until aftermarket converters made the use of ordinary recorders possible.
Because of its digital format the Datasette is both more reliable than other data cassette systems and very slow, transferring data at around 50 bytes per second. After the Datasette’s launch, however, special turbo tape software appeared, providing much faster tape operation (loading and saving). Such software was integrated into most commercial prerecorded applications (mostly games), as well as being available separately for loading and saving the users’ homemade programs and data. These programs were only widely used in Europe, as the US market had long since moved onto disks.
Datasettes can typically store about 100 kByte per 30 minute side. The use of turbo tape and other fast loaders increased this number to roughly 1000 kByte.
The Datasette has only one connection cable, with a 0.156-inch (4.0 mm)–spacing PCB edge connector at the computer end. All input/output signals to the Datasette are all digital, and so all digital-to-analog conversion, and vice versa, is handled within the unit. Power is also included in this cable. The pinout is ground, +5 V DC, motor, read, write, key-sense. The sense signal monitors the play, rewind, and fast-forward buttons but cannot differentiate between them. A mechanical interlock prevents any two of them from being pressed at the same time. The motor power is derived from the computer’s unregulated 9 V DC supply via a transistor circuit.