The Programmer's Workbench (PWB/UNIX) was an early, now discontinued, version of the Unix operating system that had been created in the Bell Labs Computer
(such as PWB/UNIX and MERT) whose code-base had diverged from the primary CSRC version. However, that term was little-used until Version 8 Unix, but has
systems that comply with the Single UNIX Specification (SUS). Early versions of Unix ran on PDP-11 computers. Unix systems are characterized by a modular