On early IBM personal computers, a cassette tape interface was provided to allow use of a cassette

Compact Cassette

The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel...

 audio recorder to load and save data and programs. This option was only included on the original 5150 (PC) and 4860

IBM PCjr

The IBM PCjr was IBM's first attempt to enter the home computer market. The PCjr, IBM model number 4860, retained the IBM PC's 8088 CPU and BIOS interface for compatibility, but various design and implementation decisions led the PCjr to be a commercial failure.- Features :Announced November 1,...

 (PCjr).

Few IBM PCs left the factory without a floppy disk drive installed. 5150s with just external cassette recorders for storage could only use the built-in ROM BASIC as their operating system. The ROM BIOS

IBM Cassette BASIC

IBM Cassette BASIC was a version of the Microsoft BASIC programming language licensed by IBM for the IBM PC. It was included in the BIOS ROM of the original IBM PC. Cassette BASIC provided the default user interface if there was no floppy disk drive installed, or if the boot code did not find a...

 supported cassette operations,
but DOS did not support cassette tape, but only disk drives. No market developed for commercial product distribution on cassette tape and the cassette interface was dropped on subsequent IBM models.

IBM PC cassette recording signal

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 1.0 ms timer period, (0) bit corresponds to . First of "11111111" is written. One synchronization bit "0". A synchronization byte of 0x16. 256-byte blocks of data and a 2-byte CRC

Cyclic redundancy check

A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...

is written until all data is transferred.