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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.
The basic 650 system consisted of three equipment cabinets:
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 signed 10-digit words of memory (5 character per word) — at addresses 0000 to 1999; 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 2.5 ms). 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. One specialized instruction, 'Table lookup', could high-equal compare a reference 10 digit word with 46 consecutive following words on the drum in one 5msec revolution and then switch to the next track in time for the next 46 words (there were fifty words per track/revolution). This was a feat we (who??) could not match on our one-thousand times faster binary machine in 1963.
The optional Auxiliary Unit (Type 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+49
See also: List of IBM products
Software
Software included FORTRANSIT – a version of FORTRAN which compiled to IT (an interpretive language of the time) which in turn was compiled to SOAP (Symbolic Optimized Assembler Program) which generated machine language statements one-for-one. Other software included BLIS (Bell Laboratories Interpretive System), which used a numeric-only three-address approach, and SPACE (Simplified Programming Anyone Can Enjoy) which was a business-oriented two-step compiler (through SOAP).
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
- The IBM 650 at Columbia University
- An IBM 650 Simulator
- IBM Museum Sindelfingen (has the working IBM 650 pictured above)
- IBM 650 documents at Bitsavers.org (PDF files)
"IBM 650"