The IBM 650 was one of IBM’s early computers, and the world’s first mass-produced computer. Over 2000 systems were produced between its introduction in 1954 and its final manufacture in 1962.

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.

IBM 650 front panel, showing bi-quinary indicators

IBM 650 front panel, rear view

The basic 650 system consisted of three equipment cabinets:

• Console Unit (Type 650)
• Power Unit (Type 655)
• Card Reader/Punch Unit (Type 533 or Type 537)

Optional equipment cabinets:

• Disk Unit (Type 355)
• Card Reader Unit (Type 543)
• Card Punch Unit (Type 544)
• Control Unit (Type 652)
• Auxiliary Unit (Type 653)
• Auxiliary Alphabetic Unit (Type 654)
• Magnetic Tape Unit (Type 727)
• Inquiry Station (Type 838)

The rotating drum memory provided 2,000 10-digit words of memory, but was quite slow because a word could not be accessed until its location on the drum surface passed under the read/write heads during rotation (the average access time was 2.5ms). Because of this, 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.

The optional Auxiliary Unit (Type 653), providing 60 10-digit words of magnetic core, was introduced on May 3, 1955 to provide a small fast memory (this device gave a memory access time of 96µs, a 26-fold raw improvement relative to the rotating drum).

The IBM 650 (pictured here) at the Haus zur Geschichte der IBM Datenverarbeitung is still running and will process an income tax program of the time, with input and output on punched cards.

See also: List of IBM products

References

• IBM (1955). IBM 650 magnetic drum data-processing machine manual of operation. IBM documentation. Form 22-6060-1 (3-57: 10M-VO).

External links

• IBM Archives: Workhorse of Modern Industry: The IBM 650 (http://www-1.ibm.com/ibm/history/exhibits/650/650_intro.html)
• The IBM 650 at Columbia University (http://www.columbia.edu/acis/history/650.html)
• An IBM 650 Simulator (http://infinitefish.com/650/650.html)
• Haus zur Geschichte der IBM Datenverarbeitung (German) (http://www.netmuseum.de/m-ausgabe.asp?strAufrufer=Liste&strId=791)