The Free On-line Dictionary of Computing (30 December 2018):
A large, scientific computer made by IBM and used
by the largest commercial, government and educational
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
[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?]