Columbus UNIX, or CB UNIX, is a discontinued variant of the UNIX operating system used internally at Bell Labs^[1] for administrative databases and transaction processing.^[2] It was developed at the Columbus, Ohio branch, based on V6, V7 and PWB Unix.^[3] It was little-known outside the company.

CB UNIX was developed to address deficiencies inherent in Research Unix, notably the lack of interprocess communication (IPC) and file locking, considered essential for a database management system. Several Bell System operation support system products were based on CB UNIX such as Switching Control Center System. The primary innovations were power-fail restart, line disciplines, terminal types, and IPC features.^[4]

The interprocess communication features developed for CB UNIX were message queues, semaphores and shared memory support. These eventually appeared in mainstream Unix systems starting with System V in 1983, and are now collectively known as System V IPC.^[2]