[1] It was common for home computers of the time, such as the Apple II, Commodore 64 and BBC Micro, to use cassette tapes for storage due to the lower cost of hardware and media compared to floppy disks.
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 drive.
[5] The IBM PCjr was also seldom sold without a floppy disk drive, but it also had two ROM cartridge slots for loading commercial software, which offered better convenience and reliability.
BIOS interrupt call 15h routines are documented in the technical reference manual that turns the cassette motor on and off, and read or write data.
[7][8] The technical reference for the IBM PC 5150 specifies that the WRITE-BLOCK routine turns on the cassette drive motor and transforms each byte into bits.