APA (7th ed.) Citation

(1988). IBM disk operating system, version 4.0. Perfect Bound Pub.

Chicago Style (17th ed.) Citation

IBM Disk Operating System, Version 4.0. Quezon City: Perfect Bound Pub, 1988.

MLA (9th ed.) Citation

IBM Disk Operating System, Version 4.0. Perfect Bound Pub, 1988.