IBM 704
IBM 704
(computer)The IBM 704 had 36-bit memory words, 15-bit addresses andinstructions with one address. A few index registerinstructions had the infamous 15-bit decrement field inaddition 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'smagnetic drum storage as they provided random access atelectronic speed to core storage, typically 32k words of 36bits each.
A typical 700 series installation would be in a speciallybuilt room of perhaps 1000 to 2000 square feet, with cablesrunning under a raised floor and substantial air conditioning.There might be up to eight magnetic tape transports, eachabout 3 x 3 x 6 feet, on one or two "channels." The 1/2 inchtape had seven tracks and moved at 150 inches per second,giving a read/write speed of 15,000 six bit characters (plusparity) per second.
In the centre would be the operator's console consisting ofcabinets 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 couldbe entered via punched cards at the console, but as a rulethe user jobs were transferred from cards to magnetic tapeby off-line equipment and only control information wasentered at the console (see SPOOL). Before each job, theoperating system was loaded from a read-only system tape(because the system in core could have been corrupted by theprevious user), and then the user's program, in the form ofcard images on the input tape, would be run. Program outputwould be written to another tape (typically on anotherchannel) for printing off-line.
Well run installations would transfer the user's cards totape, run the job, and print the output tape with a turnaroundtime of one to four hours.
The processing unit typically occupied a position symmetricbut opposite the operator's console. Physically the largestof the units, it included a glass enclosure a few feet indimension in which could be seen the "core" about one foot oneach side. The 36-bit word could hold two 18-bit addressescalled 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 andoperator's console would be a desk and bookshelves for theever-present (24 hours a day) "field engineer" dressed in, youguessed it, a grey flannel suit and tie. The maintenance ofthe many thousands of vacuum tubes, each with limitedlifetime, and the cleaning, lubrication, and adjustment ofmechanical equipment, was augmented by a constant flow ofbug reports, change orders to both hardware and software,and hand-holding for worried users.
The 704 was oriented toward scientific work and includedfloating point hardware and the first Fortranimplementation. Its hardware was the basis for therequirement in some programming languages that loops must beexecuted at least once.
The IBM 705 was the business counterpart of the 704. The705 was a decimal machine with a circular register which couldhold several variables (numbers, values) at the same time.
Very few 700 series computers remained in service by 1965, butthe IBM 7090, using transistors but similar in logicalstructure, remained an important machine until the productionof the earliest integrated circuits.