资料来源 : Free On-Line Dictionary of Computing

IBM 704
     
         A large, scientific computer made by {IBM} and used
        by the largest commercial, government and educational
        institutions.
     
        The IBM 704 had 36-bit memory words, 15-bit addresses and
        instructions with one address.  A few {index register}
        instructions had the infamous 15-bit decrement field in
        addition to the 15-bit address.
     
        The 704, and {IBM 709} which had the same basic architecture,
        represented a substantial step forward from the {IBM 650}'s
        {magnetic drum} storage as they provided random access at
        electronic speed to {core storage}, typically 32k words of 36
        bits each.
     
        [Or did the 704 actually come *before* the 650?]
     
        A typical 700 series installation would be in a specially
        built room of perhaps 1000 to 2000 square feet, with cables
        running under a raised floor and substantial air conditioning.
        There might be up to eight {magnetic tape} transports, each
        about 3 x 3 x 6 feet, on one or two "channels."  The 1/2 inch
        tape had seven tracks and moved at 150 inches per second,
        giving a read/write speed of 15,000 six bit characters (plus
        parity) per second.
     
        In the centre would be the operator's {console} consisting of
        cabinets and tables for storage of tapes and boxes of cards;
        and a {card reader}, a {card punch}, and a {line printer},
        each perhaps 4 x 4 x 5 feet in dimension.  Small {jobs} could
        be entered via {punched cards} at the console, but as a rule
        the user jobs were transferred from cards to {magnetic tape}
        by {off-line} equipment and only control information was
        entered at the console (see {SPOOL}).  Before each job, the
        {operating system} was loaded from a read-only system tape
        (because the system in {core} could have been corrupted by the
        previous user), and then the user's program, in the form of
        card images on the input tape, would be run.  Program output
        would be written to another tape (typically on another
        channel) for printing off-line.
     
        Well run installations would transfer the user's cards to
        tape, run the job, and print the output tape with a turnaround
        time of one to four hours.
     
        The processing unit typically occupied a position symmetric
        but opposite the operator's console.  Physically the largest
        of the units, it included a glass enclosure a few feet in
        dimension in which could be seen the "core" about one foot on
        each side.  The 36-bit word could hold two 18-bit addresses
        called the "Contents of the Address Register" ({CAR}) and the
        "Contents of the Decrement Register" ({CDR}).
     
        On the opposite side of the floor from the tape drives and
        operator's console would be a desk and bookshelves for the
        ever-present (24 hours a day) "field engineer" dressed in, you
        guessed it, a grey flannel suit and tie.  The maintenance of
        the many thousands of {vacuum tubes}, each with limited
        lifetime, and the cleaning, lubrication, and adjustment of
        mechanical equipment, was augmented by a constant flow of
        {bug} reports, change orders to both hardware and software,
        and hand-holding for worried users.
     
        The 704 was oriented toward scientific work and included
        {floating point} hardware and the first {Fortran}
        implementation.  Its hardware was the basis for the
        requirement in some programming languages that loops must be
        executed at least once.
     
        The {IBM 705} was the business counterpart of the 704.  The
        705 was a decimal machine with a circular register which could
        hold several variables (numbers, values) at the same time.
     
        Very few 700 series computers remained in service by 1965, but
        the {IBM 7090}, using {transistors} but similar in logical
        structure, remained an important machine until the production
        of the earliest {integrated circuits}.
     
        [Was the 704 scientific, business or general purpose?
        Difference between 704 and 709?]
     
        (1996-01-24)