IBM 704
<computer> 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)
Nearby terms:
IBM 650 « IBM 700 series « IBM 701 « IBM 704
» IBM 7040 » IBM 705 » IBM 709
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