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 ...

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 ...

includes support for storing data and programs on

compact cassette tape The Compact Cassette, also commonly called a cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Ottens and his team at the Dutch company Ph ...

. It was common for

home computers Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

of the time, such as the

Apple II Apple II ("apple Roman numerals, two", stylized as Apple ][) is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The Apple II (original), original Apple II model, which gave the series its name, was designed ...

, Commodore 64 and BBC Micro, 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 1980s. ''

BYTE The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

'' asked in 1982, "I'm still looking for someone who uses BM cassette tape Did IBM seriously think its system would compete with the

VIC-20 The VIC-20 (known as the VC-20 in Germany and the VIC-1001 in Japan) is an 8-bit entry level home computer that was sold by Commodore International, Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commod ...

and

ZX81 The ZX81 is a home computer that was produced by Sinclair Research and manufactured in Dundee, Scotland, by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and designed to be a low-c ...

?" The IBM PC cassette format was not popular since very few were shipped without at least one

floppy disk drive A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a 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 with a ...

, and apart from one diagnostic tape available from

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

, there seems never to have been any software sold on tape except IBM Typing Tutor created by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

, and the interface was not included on the follow-up

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 simi ...

. 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, a diskette, or a disk) is a 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 with a ...

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, cassette, 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, ...

slots for loading commercial software, which offered better convenience and reliability.

Use

An IBM PC with just an external cassette recorder for storage can only use the built-in

ROM BASIC The IBM Personal Computer BASIC, commonly shortened to IBM BASIC, is a programming language first released by IBM with the IBM Personal Computer, Model 5150 (IBM PC) in 1981. IBM released four different versions of the Microsoft BASIC interpre ...

as its

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

, which supports cassette operations.

IBM PC DOS IBM PC DOS (an acronym for IBM Personal Computer Disk Operating System),Formally known as "The IBM Personal Computer DOS" from versions 1.0 through 3.30, as reported in those versions' respective COMMAND.COM outputs also known as PC DOS or IBM ...

has no native support for cassette tapes, though software can be written to provide support.

BIOS interrupt call BIOS implementations provide interrupts that can be invoked by operating systems and application programs to use the facilities of the firmware on IBM PC compatible computers. Traditionally, BIOS calls are mainly used by DOS programs and some ot ...

15 h routines are documented in the technical reference manual that turns the cassette motor on and off, and read or write data. Data is written with a lead-in section, and formatted in 256-

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

blocks with a 2-byte CRC. Programmers can also operate the cassette relay by writing to its

I/O address Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer (often mediating access via chipset). An alterna ...

. The cassette, disk, advanced, and cartridge versions of

IBM BASIC The IBM Personal Computer BASIC, commonly shortened to IBM BASIC, is a programming language first released by IBM with the IBM Personal Computer, Model 5150 (IBM PC) in 1981. IBM released four different versions of the Microsoft BASIC interprete ...

includes statements for cassette operations, but these features only work if the machine had a cassette port. The data transfer speed is from 1-2

kilobit The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...

s per second, compared to the disk drive's 250 kilobits per second. In 2020, the cassette interfaces of the IBM PC and PCjr were utilized to boot

FreeDOS FreeDOS (formerly PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running Legacy system, legacy software and supporting embedded systems. FreeDOS ca ...

off a custom

vinyl disc A phonograph record (also known as a gramophone record, especially in British English) or a vinyl record (for later varieties only) is an analog signal, analog sound Recording medium, storage medium in the form of a flat disc with an inscribed, ...

Data format

The technical reference for the specifies that the WRITE-BLOCK routine turns on the cassette drive motor and transforms each byte into

bit The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...

s. A (1) bit corresponds to a timer period, (0) bit corresponds to , which results in a recording speed of . First of is written. One synchronization bit . A synchronization byte of . 256-byte blocks of data and a 2-byte CRC is written until all data is transferred.

Connector pinout

The IBM PC uses a female 5-pin

DIN connector The DIN connector is an electrical signal connector that was standardized by the (DIN), the German Institute for Standards, in the mid 1950s, initially with three pins for mono, but when stereo connections and gear appeared in the late 1950s, v ...

(the same as the keyboard connector) for the cassette port: Pinout: * 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 In telecommunications and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...

) * Pin 5: DATA-OUT (250 μA jumperable either at 0.68 V (" AUX") or 75 mV (" MIC")) Motor control: 8255A port , bit : = on, = off.

References

{{Magnetic tape data formats Home computer peripherals IBM storage devices Computer storage tape media

Use

Data format

Connector pinout

See also

References