<operating system> A version of Unix based on the Berkeley
version, designed and implemented by DEC to run on their
VAX and DECstation processors.
(1994-10-26)
Wikipedia
Ultrix
Ultrix (officially all-caps ULTRIX) is the brand name of Digital Equipment Corporation's (DEC) discontinued native Unix operating systems for the PDP-11, VAX, MicroVAX and DECstations.