Ultrix is a computer operating system of the Unix -family by Digital Equipment Corporation to run on their workstations.

Ultrix runs on DECstation workstations, which are built atop MIPS R2000 and R3000 family of RISC processors, and on DEC VAX-machines.

It's basically a BSD 4.2, with some features from 4.3 and System V Release 2. It supports TCP/IP and DECnet networking and DEC's X window system called DECwindows.

The first version of Ultrix, 1.0, was released early 1980s, and the last version, 4.5, was released in November 1995. After this the DEC's Unix-product was DEC OSF/1 AXP, also known as Digital UNIX, which is an implementation of Open Software Foundation's OSF/1 for the DEC Alpha architecture.