Source : Free On-Line Dictionary of Computing

PDP-7
     
         A minicomputer sold by DEC in 1964.  It had a
        memory cycle time of 1.75 microseconds and add time of 4
        microseconds.  I/O included a keyboard, printer, {paper-tape}
        and dual transport DECtape drives (type 555).
     
        DEC provided an "advanced" {Fortran II} {compiler}, a Symbolic
        {Assembler}, Editor, {DDT} Debugging System, Maintenance
        routines and a library of arithmetic, utility and programming
        aids developed on the program-compatible {PDP-4}.
     
        [DEC sales brochure].
     
        The PDP-7 was considered reliable enough (when properly
        programmed) to be used for control of nuclear reactors and
        such.
     
        Around 1970 {Ken Thompson} built the {operating system} that
        became {Unix} on a scavenged {PDP-7} so he could play a
        descendant of the {SPACEWAR} game.
     
        (1995-03-10)