Page "History of operating systems" Paragraph 37

While many 8-bit home computers of the 1980s, such as the Commodore 64, Apple II series, the Atari 8-bit, the Amstrad CPC, ZX Spectrum series and others could load a third-party disk-loading operating system, such as CP / M or GEOS, they were generally used without one.

Their built-in operating systems were designed in an era when floppy disk drives were very expensive and not expected to be used by most users, so the standard storage device on most was a tape drive using standard compact cassettes.

Most, if not all, of these computers shipped with a built-in BASIC interpreter on ROM, which also served as a crude command line interface, allowing the user to load a separate disk operating system to perform file management commands and load and save to disk.

The most popular home computer, the Commodore 64, was a notable exception, as its DOS was on ROM in the disk drive hardware, and the drive was addressed identically to printers, modems, and other external devices.