Editing IBM 650 (section)

==Hardware==
The basic 650 system consisted of three units:<ref name=650c>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_cm1.html |title=IBM Archives: 650 Components |archive-url=https://web.archive.org/web/20230725133256/https://www.ibm.com/ibm/history/exhibits/650/650_cm1.html |archive-date=2023-07-25 |url-status=dead}}</ref>

* IBM 650 Console Unit<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph01.html |title=IBM Archives: IBM 650 Console Unit |website=IBM |archive-url=https://web.archive.org/web/20231023164304/https://www.ibm.com/ibm/history/exhibits/650/650_ph01.html |archive-date=2023-10-23 |url-status=dead}}</ref> housed the magnetic drum storage, arithmetical device (using vacuum tubes) and the operator's console.
* [[IBM 655]] Power Unit<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph15.html |title=IBM Archives: IBM 655 Power Unit |website=IBM |archive-url=https://web.archive.org/web/20230408154257/https://www.ibm.com/ibm/history/exhibits/650/650_ph15.html |archive-date=2023-04-08 |url-status=dead}}</ref>
* [[IBM 533]] or [[IBM 537]] Card Read Punch Unit<ref>Other IBM names for the 533 included ''Input-Output Unit'' and ''Read-Punch Unit''.</ref><ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph13.html |title=IBM Archives: IBM 533 Card Read Punch |website=IBM |archive-url=https://web.archive.org/web/20230408161301/https://www.ibm.com/ibm/history/exhibits/650/650_ph13.html |archive-date=2023-04-08 |url-status=dead}}</ref><ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph14.html |title=IBM Archives: IBM 537 Card Read Punch |website=IBM |archive-url=https://web.archive.org/web/20230409012830/https://www.ibm.com/ibm/history/exhibits/650/650_ph14.html |archive-date=2023-04-09 |url-status=dead}}</ref> The IBM 533 had separate feeds for reading and punching; the IBM 537 had one feed, thus could read and then punch into the same card.
Weight: {{convert|5400-6263|lb|ST MT|1}}.<ref>{{cite book |title=Physical Planning Installation Manual 650 System |url=http://www.bitsavers.org/pdf/ibm/650/21-7643-1_650_InstallMan.pdf |page=32 |publisher=IBM |via=Bitsavers |date=October 1, 1957 |access-date=May 31, 2018}}</ref><ref>{{cite book |title=Customer Engineering Manual of Instruction |url=http://www.bitsavers.org/pdf/ibm/650/22-6284-1_650_CE_Manual_of_Instruction.pdf |page=I-17 |publisher=IBM |via=Bitsavers |year=1956 |access-date=May 31, 2018}}</ref>

Optional units:<ref name=650c/>

* IBM 46 Tape To Card Punch, Model 3<ref name=650c />
* IBM 47 Tape To Card Printing Punch, Model 3<ref name=650c />
* [[IBM 355]] Disk Storage Unit<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph07.html |title=IBM Archives: IBM 355 Disk Storage |website=IBM |archive-url=https://web.archive.org/web/20230409022452/https://www.ibm.com/ibm/history/exhibits/650/650_ph07.html |archive-date=2023-04-09 |url-status=dead}}</ref>  Systems with a disk unit were known as ''IBM 650 RAMAC Data Processing Systems''
* [[IBM 407]] Accounting Machine<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/vintage/vintage_4506VV4007.html |title=IBM Archives: IBM 407 accounting machine |website=IBM |archive-url=https://web.archive.org/web/20230703223109/https://www.ibm.com/ibm/history/exhibits/vintage/vintage_4506VV4007.html |archive-date=2023-07-03 |url-status=dead}}</ref>
* [[IBM 543]] Card Reader Unit
* [[IBM 544]] Card Punch Unit
* [[IBM 652]] Control Unit (magnetic tape, disk)<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph12.html |title=IBM Archives: IBM 652 Control Unit |website=IBM |archive-url=https://web.archive.org/web/20230408162804/https://www.ibm.com/ibm/history/exhibits/650/650_ph12.html |archive-date=2023-04-08 |url-status=dead}}</ref>
* [[IBM 653]] Storage Unit (magnetic tape, disk, core storage, index registers, [[floating-point arithmetic]])<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph11.html |title=IBM Archives: IBM 653 Auxiliary Unit |website=IBM |archive-url=https://web.archive.org/web/20230409012811/https://www.ibm.com/ibm/history/exhibits/650/650_ph11.html |archive-date=2023-04-09 |url-status=dead}}</ref>
* [[IBM 654]] Auxiliary Alphabetic Unit
* [[IBM 727]] Magnetic Tape Unit
* [[IBM 838]] Inquiry Station<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph16.html |title=IBM Archives: IBM 838 Inquiry Station |website=IBM |archive-url=https://web.archive.org/web/20230408112022/https://www.ibm.com/ibm/history/exhibits/650/650_ph16.html |archive-date=2023-04-08 |url-status=dead}}</ref>

===Main memory===
Rotating [[drum memory]] provided 1,000, 2,000, or 4,000 [[Word (computer architecture)|words]] of memory at addresses 0000 to 0999, 1999, or 3999 respectively. Each word had 10 [[Bi-quinary coded decimal#IBM650code|bi-quinary coded decimal digits]], representing a signed 10-digit number or five characters. (Counting a bi-quinary coded digit as seven bits, 4000 words would be equivalent to 35 kilobytes.)<ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_ph09.html |title=IBM Archives: IBM 650 Magnetic Drum |website=IBM |archive-url=https://web.archive.org/web/20230207023510/https://www.ibm.com/ibm/history/exhibits/650/650_ph09.html |archive-date=2023-02-07 |url-status=dead}}</ref><ref>{{cite web |url=https://www.ibm.com/ibm/history/exhibits/650/650_pr4.html |title=IBM Archives: IBM 650 Model 4 announcement |website=IBM |archive-url=https://web.archive.org/web/20231023160555/https://www.ibm.com/ibm/history/exhibits/650/650_pr4.html |archive-date=2023-10-23 |url-status=dead}}</ref>  Words on the drums were organized in bands around the drum, fifty words per band, and 20, 40, or 80 bands for the respective models. A word could be accessed when its location on the drum surface passed under the read/write heads during rotation (rotating at 12,500 [[Revolutions per minute|rpm]], the non-optimized average access time was 2.5 [[millisecond|ms]]).  Because of this timing, the second address in each instruction was the address of the next instruction.  Programs could then be [[Optimum programming|optimized]] by placing instructions at addresses that would be immediately accessible when execution of the previous instruction was completed. IBM provided a form with ten columns and 200 rows to allow programmers to keep track of where they put instructions and data. Later an [[assembly language|assembler]], SOAP (Symbolic Optimal Assembly Program), was provided that performed rough optimization.<ref>{{cite web|url=https://www.drdobbs.com/the-ibm-650/184404809|title=The IBM 650|first=Herb|last=Kugel|date=October 22, 2001|publisher=Dr. Dobb's}}</ref><ref name=soap />

The [[LGP-30]], [[Bendix G-15]] and [[IBM 305 RAMAC]] computers used vacuum tubes and drum memory too, but they were quite different from the IBM 650.

Instructions read from the drum went to a ''program register'' (in current terminology, an [[instruction register]]). Data read from the drum went through a 10-digit ''distributor.'' The 650 had a 20-digit [[Accumulator (computing)|''accumulator'']], divided into 10-digit lower and upper accumulators with a common sign.  Arithmetic was performed by a one-digit adder.  The console (10 digit switches, one sign switch, and 10 bi-quinary display lights), distributor, lower and upper accumulators were all addressable; 8000, 8001, 8002, 8003 respectively.

===IBM 653 Storage Unit===
The optional IBM 653 Storage Unit, was introduced on May 3, 1955, ultimately providing up to five features:<ref name=CPU-ext/>

* Magnetic tape controller (for IBM 727 Magnetic Tape units) (10 extra operation codes)
* Disk storage controller (1956 enhancement for then new IBM 355 Disk Storage Unit) (five extra operation codes)
* Sixty 10-digit words of [[core memory|magnetic core]] memory at addresses 9000 to 9059. This small ''fast memory'' had an access time of 96[[microsecond|μs]], a 26-fold improvement relative to the rotating drum. This feature added five operation codes and was needed as a buffer for tape and disk I/O. The 60 words could also be used by programs to speed up inner loops and table lookups.
* Three four-digit [[index register]]s 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 drum then indexing was by adding 4000 to the first address for index register A, adding 4000 to the second address for index register B, and by adding 4000 to each of the two addresses for index register C (the indexing for 4000-word systems only applied to the first address). The 4000-word systems required [[Transistor computer|transistorized]] read/write circuitry for the drum memory and were available before 1963. (18 extra operation codes)
* [[Floating point]] – arithmetic instructions supported an eight-digit mantissa and two-digit characteristic (offset exponent) – '''MMMMMMMMCC''', providing a range of ±0.00000001E-50 to ±0.99999999E+49. (seven extra operation codes)