IBM 650

IBM 650

The IBM 650 ( [ photo] ) was one of IBM’s early computers, and the world’s first mass-produced ( [ photo] ) computer. It was announced in 1953, and over 2000 systems were produced between the first shipment in 1954 and its final manufacture in 1962. Support for the 650 and its component units was withdrawn in 1969.

The 650 is a two-address, bi-quinary coded decimal machine (both data and addresses were decimal), with memory on a rotating drum. The 650 was specifically designed for users of existing IBM unit record equipment (electro-mechanical punched card-processing machines) upgrading from so-called Calculating Punches, like the IBM 604 model, to computers proper.

One of the 650's most significant features was that, if processing was interrupted by a "random processing error" (hardware glitch), the machine could automatically resume from the last checkpoint instead of requiring the operators to restart the job manually from the beginning.


The basic 650 system consisted of three components:
*Console Unit ( [ IBM 650] )
*Power Unit ( [ IBM 655] )
*Card Reader/Punch Unit ( [ IBM 533] or [ IBM 537] )Optional components:
*Disk Unit ( [ IBM 355] ) Systems with a disk unit were known as a "IBM RAMAC 650 Data Processing System"
*Card Reader Unit (IBM 543)
*Card Punch Unit (IBM 544)
*Control Unit ( [ IBM 652] ) Magnetic Tape Controller
*Auxiliary Unit ( [ IBM 653] ) Core storage, index registers, floating point arithmetic
*Auxiliary Alphabetic Unit (IBM 654)
*Magnetic Tape Unit ( [ IBM 727] )
*Inquiry Station ( [ IBM 838] )
*Tape To Card Punch IBM 46 Model 3
*Tape To Card Punch IBM 47 Model 3
*Alphabetical Accounting Machine IBM 407

The rotating drum memory ( [ photo] ) provided 2,000 signed 10-digit words of memory (5 character per word) at addresses 0000 to 1999. It was, by 21st Century standards, quite slow because a word could not be accessed until its location on the drum surface passed under the read/write heads during rotation (rotating at 12,500 rpm, the non-optimized average access time was 2.5 ms). Because of this timing restriction, the second address in each instruction word was the address of the next instruction. Programs could be "optimized" by placing instructions around the drum based on the expected execution time of the previous instruction. One specialized instruction, 'Table lookup', could high-equal compare a reference 10 digit word with 46 consecutive following words on the drum in one 5ms revolution and then switch to the next track in time for the next 46 words (there were fifty words per track/revolution). This feat was only three times slower than on a one-thousand times faster binary machine in 1963 (1500 microsecs on the IBM7040 to 5000 microsecs on the IBM650 for looking up 46 entries as long as both were programmed in assembler. One higher level language made the IBM7040 dramatically slower at table-look-up.An upgraded 4,000 word drum became available in 1959.

The optional Auxiliary Unit (IBM 653), was introduced on May 3, 1955, providing up to three features:
*60 10-digit words of magnetic core memory at addresses 9000 to 9059; a small "fast memory" (this device gave a memory access time of 96µs, a 26-fold raw improvement relative to the rotating drum), needed for a tape and disk I/O buffer
*3 4-digit index registers at addresses 8005 to 8007; drum addresses were indexed by adding 2000, 4000 or 6000 to them, core addresses were indexed by adding 0200, 0400 or 0600 to them. If the system had the 4000 word memory drum then indexing was by adding 4000 to the first address for index reg A, adding 4000 to the second address for index reg B, and by adding 4000 to each of the two addresses for index reg C. (the indexing for 4000 word systems only applied to the first address). The 4000 word systems required transistorized read/write circuitry for the drum memory and were available before 1963.
*Floating point – arithmetic instructions with 8 digit mantissa and 2 digit characteristic (offset exponent) – MMMMMMMMCC, providing a range of ±0.10000000E-50 to ±0.99999999E+49The IBM 533 reader punch unit could only read a maximum of 26 columns of alphnumerics from cards in mostly fixed columns. An expansion allowed more but certainly not over 50, as only ten words could be read from a card (5 characters per word).

The IBM 650 (pictured here) at the "Haus zur Geschichte der IBM Datenverarbeitung" (House for the History of IBM Data Processing), Sindelfingen, is still running (as of May 2004) and will process an income tax program of the time, with input and output on punched cards.

The IBM 7070, announced 1960, was designed to provide a "transistorized IBM 650" upgrade path. The IBM 1620, introduced in 1959, addressed the lower end of the market. Both were decimal machines.

ee also

*List of IBM products


Software included:
* [ BLIS] (Bell Laboratories Interpretive System) [HOPL shows the name as "BLISS"; a definitive source has not been located] , which used a numeric-only three-address approach
* [ IPL] the first list processing language.
* [ SPACE] (Simplified Programming Anyone Can Enjoy) which was a business-oriented two-step compiler (through SOAP)
*cite book
first = A.J.
last = Perlis
coauthors = et al.
title = Internal Translator; IT, A Compiler for the 650
date = 4/18/58
url =
id = 650 Library Program 2.1.001

*cite book
last = IBM
title = SOAP II for the IBM 650
year = 1957
url =
id = C24-4000-0

*cite book
last = IBM
title = FOR TRANSIT Automatic Coding System for the IBM 650
year = 1959
url =
id = 28-4028
A version of Fortran which compiled to IT which in turn was compiled to SOAP.
*cite book
last = IBM
title = FORTRAN Automatic Coding System for the IBM 650
year = 1960
url =
id = 29-4047


*cite book
last = IBM
title =IBM 650 magnetic drum data-processing machine manual of operation.
url =
year = 1955
id =22-6060

*cite book
last = IBM
title = IBM Presents the 650 Magnetic Drum Data Processing Machine
url =
year = 1955
id = 32-6770

*cite journal
first = Donald E.
last = Knuth
title = The IBM 650: An Appreciation from the Field
journal = IEEE Annals of the History of Computing
volume = 8
issue = 1
date = January-March 1986
pages = 50–55
doi = 10.1109/MAHC.1986.10010
Donald Knuth also dedicated his series of books, "The Art of Computer Programming", to an IBM 650 computer, with the words "This series of books is affectionately dedicated / to the Type 650 computer once installed at / Case Institute of Technology, / in remembrance of many pleasant evenings."
* [ IBM 650 Magnetic Drum Data Processing Machine]

External links

* [ IBM Archives: Workhorse of Modern Industry: The IBM 650] Includes a chronology, technical specifications, representative customers, and applications the 650 was used for.
*cite book
first = Martin H.
last = Weik
title = A Third Survey of Domestic Electronic Digital Computing Systems
publisher = Ballistic Research Laboratories (BRL)
date = March 1961
id = Report No. 1115
url =
Includes about 40 pages of IBM 650 survey detail: customers, applications, specifications, and costs.
* [ The IBM 650 at Columbia University]
* [ An IBM 650 Simulator]
* [ Sindelfingen] Scroll down to "House for the History of the IBM data processing" where the working IBM 650 pictured above is located. See also [ History Galore at IBM Museum] .
* [ IBM 650 documents at] (PDF files)


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