[a]  UNICS (Version Zero)   PDP-7       Summer   1969
    [b]  First Edition UNIX     PDP-11/20   November 1971
    [c]  Fifth Edition UNIX     PDP-11/40   June     1974
    [d]  Sixth Edition UNIX     PDP-11/45   May      1975
    [e]  Seventh Edition UNIX   PDP-11/70   January  1979
    [f]  Research UNIX 8        VAX-11/780           1981
    [g]  AT&T UNIX System III   PDP-11/70   Fall     1982
    [h]  AT&T UNIX System V     PDP-11/70            1983
    [i]  AT&T UNIX System V     3b2/400              1984
    [j]  4.3  BSD               MicroVAX    June     1986
    [k]  2.11 BSD               PDP-11/70   January  1992