AT&T announced System III in late 1981,[2] and it was first released outside of Bell Labs in 1982.

System III supported the DEC PDP-11 and VAX computers.

It also combined various improvements to Version 7 Unix by outside organizations.

However, it did not include notable additions made in BSD such as the C shell (csh) and screen editing.

Third-party variants of System III include (early versions of) HP-UX, IRIX, IS/3 and PC/IX, PC-UX, PNX, SINIX, Venix and Xenix.