The original
IBM Personal Computer
The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a tea ...
and
IBM PCjr
The IBM PCjr (pronounced "PC junior") was a home computer produced and marketed by IBM from March 1984 to May 1985, intended as a lower-cost variant of the IBM PC with hardware capabilities better suited for video games, in order to compete mor ...
included support for storing data and programs on
compact cassette tape.
It was common for
home computers of the time, such as the
Apple II
The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-m ...
,
Commodore 64
The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness W ...
and
BBC Micro
The British Broadcasting Corporation Microcomputer System, or BBC Micro, is a series of microcomputers and associated peripherals designed and built by Acorn Computers in the 1980s for the BBC Computer Literacy Project. Designed with an emphas ...
, to use cassette tapes for storage due to the lower cost of hardware and media compared to floppy disks. A wide range of commercial home computer software was available on tape throughout the 80s.
The IBM PC cassette format did not experience the same popularity however, since very few were shipped without at least one
floppy disk drive, and apart from one diagnostic tape available from IBM, there seems never to have been any software sold on tape, and the interface was not included on the followup
PC XT
The IBM Personal Computer XT (model 5160, often shortened to PC/XT) is the second computer in the IBM Personal Computer line, released on March 8, 1983. Except for the addition of a built-in hard drive and extra expansion slots, it is very simil ...
. Despite this lack of popularity, up until the original PC's discontinuation in 1987, IBM continued to offer a Model 104 which shipped without a
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined ...
drive.
The IBM PCjr was also seldom sold without a floppy disk drive, but it also had two
ROM cartridge
A ROM cartridge, usually referred to in context simply as a cartridge, cart, or card, is a replaceable part designed to be connected to a consumer electronics device such as a home computer, video game console or, to a lesser extent, elect ...
slots for loading commercial software, which offered better convenience and reliability.
Use
An IBM PC with just an external cassette recorder for storage could only use the built-in
ROM BASIC as its operating system, which supported cassette operations.
IBM PC DOS had no support for cassette tape, though software could have been written by the user to provide support.
BIOS interrupt call 15
h routines were documented in the technical reference manual that would turn the cassette motor on and off, and read or write data. Data was written with a lead-in section, and formatted in 256-byte blocks with a 2-byte
CRC.
Programmers could also operate the cassette relay by writing to its I/O address. The cassette, disk, advanced, and cartridge versions of
IBM BASIC included statements for cassette operations, but these features only worked if the machine had a cassette port.
The data transfer speed was from 1-2 kilobits per second, compared to the disk drive's 250 kilobits per second.
Data format
The technical reference for the specifies that the WRITE-BLOCK routine turns on the cassette drive motor and transforms each byte into bits. A (1) bit corresponds to a timer period, (0) bit corresponds to , which results in a recording speed of .
First of "11111111" is written. One synchronization bit "0". A synchronization byte of 0x16. 256-byte blocks of data and a 2-byte
CRC is written until all data is transferred.
[ 091207]
Connector pinout
The IBM PC used a female 5-pin
DIN connector
The DIN connector is an electrical connector that was standardized by the ' (DIN), the German Institute for Standards, in the early 1970s. The male DIN connectors (plugs) feature a 13.2 mm diameter metal shield with a notch that limits the ...
(the same as the keyboard connector) for the cassette port:
Pinout:[IBM (1983). ''IBM PC Technical Reference Handbook''. Comment: Also includes a complete listing of the ROM BIOS source code and schematics of the original IBM PC.]
* Pin 1: MOTOR CONTROL COMMON
* Pin 2: GND
* Pin 3: MOTOR CONTROL (6 V/1 A) RELAY
* Pin 4: DATA-IN (500 nA with 13 V at 1000-2000 Baud)
* Pin 5: DATA-OUT (250 µA jumperable either at 0.68 V ("AUX") or 75 mV ("MIC"))
Motor control:
8255A port , bit 3: 0 = on, 1 = off.
See also
*
IBM Cassette BASIC
*
Commodore Datasette
*
Kansas City standard
*
Tarbell Cassette Interface
References
{{Magnetic tape data formats
Home computer peripherals
IBM storage devices
Tape-based computer storage