Editing IBM 1620 (section)

==Development history==
===A computer for the "small scientific market"===
In 1958 IBM assembled a team at the [[Poughkeepsie, New York]] development laboratory to study the "small scientific market". Initially the team consisted of Wayne Winger (Manager), Robert C. Jackson, and William H. Rhodes.

====Requirements and design====
The competing computers in this market were the [[Librascope LGP-30]] and the [[Bendix&nbsp;G-15]]; both were [[drum memory]] machines. IBM's smallest computer at the time was the popular [[IBM&nbsp;650]], a fixed word length decimal machine that also used drum memory. All three used [[vacuum tube]]s. It was concluded that IBM could offer nothing really new in that area. To compete effectively would require use of technologies that IBM had developed for larger computers, yet the machine would have to be produced at the least possible cost.

To meet this objective, the team set the following requirements:
* Core memory
* Restricted instruction set
** No divide or floating-point instructions, use subroutines in the "general program package"
* Wherever possible replace hardware with existing logical machine functions
** No arithmetic circuits, use tables in core memory
* Least expensive Input/Output possible
** No punch cards, use paper tape
** No printer, use operator's console typewriter

====The prototype====
The team expanded with the addition of Anne Deckman, Kelly B. Day, William Florac, and James Brenza. They completed the [[#CADET|(codename) CADET]] prototype in the spring of 1959.

Meanwhile, the [[San Jose, California]] facility was working on a proposal of its own. IBM could only build one of the two and the [[Poughkeepsie, New York|Poughkeepsie]] proposal won because "the San Jose version is top of the line and not expandable, while your proposal has all kinds of expansion capability - never offer a machine that cannot be expanded".

{| style="float:right;"
|-
| [[Image:IBM1620A.jpg]]
|-
| style="text-align:center;"| IBM 1620 Model I Level A (prototype), as it appeared<br/>
in the IBM announcement of the machine.
|}

Management was not entirely convinced that [[core memory]] could be made to work in small machines, so Gerry Ottaway was loaned to the team to design a [[drum memory]] as a backup. During [[acceptance testing]] by the Product Test Lab, repeated core memory failures were encountered and it looked likely that management's predictions would come true. However, at the last minute it was found that the [[muffin fan]] used to blow hot air through the core stack was malfunctioning, causing the core to pick up noise pulses and fail to read correctly. After the fan problem was fixed, there were no further problems with the core memory and the drum memory design effort was discontinued as unnecessary.

====Transferred to San Jose for production====
Following announcement of the IBM 1620 on October 21, 1959, due to an internal reorganization of IBM, it was decided to transfer the computer from the Data Processing Division at Poughkeepsie (large scale mainframe computers only) to the General Products Division at San Jose (small computers and support products only) for manufacturing.

Following transfer to San Jose, someone there jokingly suggested that the code name '''[[#CADET|CADET]]''' actually stood for "'''C'''an't '''A'''dd, '''D'''oesn't '''E'''ven '''T'''ry", referring to the use of addition tables in memory rather than dedicated addition circuitry (and SDTRL actually stood for "'''S'''old '''D'''own '''T'''he '''R'''iver '''L'''ogic" became a common joke among the CEs). This stuck and became very well known among the user community.<ref>"In 1962, IBM began delivery of a remarkable little machine originally called the Cadet but marketed as the IBM 1620." {{cite book
|title=Milestones in Computer Science and Information Technology |url=https://archive.org/details/milestonesincomp0000reil
|url-access=registration |isbn=978-1573565219|author=Edwin D. Reilly  |date=2003}}</ref><ref name=McNabbs>even five years later, it was still uncommon for a high school to have an IBM 1620: {{cite web |url=http://paul.mcnabbs.org/ibm1620 |title=IBM 1620}}</ref><ref name="IBM 1620 CADET">"The IBM 1620 (a.k.a. CADET) ...  stood for 'Can't Add and Doesn't Even Try.'"</ref>

===Implementation "levels"===
* [[IBM 1620 Model I|Model I]]
** Level A; prototype.
*** All [[Flip-flop (electronics)|flip-flop]]s in the design were [[transistor]]ized versions of the original ''Eccles-Jordan trigger circuit''. While this machine was fully functional, it was found that the [[capacitor]] coupling used in these proved troublesome in the noisy signal environment of [[relay]]s and timing [[Cam (mechanism)|cam]] driven [[switch]]es used to drive the console typewriter. This necessitated a ''complete redesign'' of the machine to use ''S-R'' flip-flops instead (except for two triggers used to generate clocks for the ''S-R'' flip-flops). However usage of the term ''Trigger'' was retained in all the documentation when referring to a flip-flop, as it was IBM's conventional term (as ''alphamerics'' was their term for alphanumerics).
*** This is the only level using a one piece vertical control panel, when the design was transferred from Poughkeepsie to San Jose it was redesigned to the two piece angled control panel used on all production models.
** Level B; first production.
*** This is the only level using a burnished aluminum lower control panel, later levels finished this panel with white.
** Level C; introduction of 1622 card reader/punch.
** Level D; introduction of 1311 disk drives and addition of optional "Gate J" containing disk control logic.
** Level E; introduction of Floating-Point option.
** Level F
** Level G; introduction of Interrupt option (needed for [[IBM 1710]]).
*** Did not support BT & BB subroutines in interrupt code!
*** Disk control logic on "Gate J" logic merged into "Gate A" & "Gate B".
**** Made possible because much of logic was compacted using cards designed for the Model II.
** Level H; improved Interrupt option that supported BT & BB subroutines in interrupt code.
*** Final version of the Model I.
* [[IBM 1620 Model II|Model II]] (no information on "Levels" available at this time)
:: The 1620 Model II introduced basic [[arithmetic logical unit|ALU]] hardware for addition and subtraction (making "'''C'''an't '''A'''dd, '''D'''oesn't '''E'''ven '''T'''ry" no longer applicable) and [[index register]]s.
* Model III
** Work was begun on a 1620 Model III but the project was quickly canceled as IBM wanted to promote sales of their new [[System/360]] and discontinue the old lines.

===Patents===
{| border="0" style="width:100%;" cellpadding="10"
|-
|  style="width:50%; vertical-align:top;"|
* {{US patent|3049295}}{{snd}} Multiplying Computer
** Patent filed: December 20, 1960
** Patent issued: August 14, 1962
** Inventors
*** William H. Rhodes
*** James G. Brenza
*** Wayne D. Winger
*** Robert C. Jackson
** Claims and prior art references
*** 21 claims
*** No prior art
** Diagrams and Text
*** 156 sheets of diagrams (Describes 1620 in full details.)
*** 31 sheets of text
* {{US patent|3328767}}{{snd}} Compact Data Lookup Table
** Patent filed: December 31, 1963
** Patent issued: June 27, 1967
** Inventors
*** Gerald H. Ottaway
** Claims and prior art references
*** 11 claims
*** 5 prior art
** Diagrams and Text
*** 5 sheets of diagrams
*** 4 sheets of text
|  style="width:50%; vertical-align:top;"|
* {{US patent|3199085}}{{snd}} Computer with Table Lookup Arithmetic Unit Feature
** Patent filed: December 20, 1960
** Patent issued: August 3, 1965
** Inventors
*** William H. Rhodes
*** James G. Brenza
*** Wayne D. Winger
** Claims and prior art references
*** 21 claims
*** 5 prior art
** Diagrams and Text
*** 156 sheets of diagrams (Describes 1620 in full details.)
*** 31 sheets of text
* {{US patent|3239654}}{{snd}} Dividing Computer
** Patent filed: February 8, 1961
** Patent issued: March 8, 1966
** Inventors
*** Robert C. Jackson
*** William A. Florac
*** Wayne D. Winger
** Claims and prior art references
*** 9 claims
*** 1 prior art
*** 3 publications
** Diagrams and Text
*** 13 sheets of diagrams
*** 19 sheets of text
|}