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)