Editing CICS (section)

===Early evolution===
CICS originally only supported a few IBM-brand devices like the 1965 [[IBM 2741]] Selectric (golf ball) typewriter-based terminal. The 1964 [[IBM 2260]] and 1972 [[IBM 3270]] [[video display terminal]]s were widely used later.

In the early days of IBM mainframes, computer software was free{{snd}} bundled at no extra charge with [[computer hardware]]. The [[OS/360]] operating system and application support software like CICS were "open" to IBM customers long before the [[open-source software]] initiative. Corporations like Standard Oil of Indiana (Amoco) made major contributions to CICS.

The IBM Des Plaines team tried to add support for popular non-IBM terminals like the [[ASCII]] [[Teletype Model 33]] ASR, but the small low-budget software development team could not afford the $100-per-month hardware to test it. IBM executives incorrectly felt that the future would be like the past, with [[batch processing]] using traditional [[punch cards]].

IBM reluctantly provided only minimal funding when public utility companies, banks and credit-card companies demanded a cost-effective interactive system (similar to the 1965 [[IBM Airline Control Program]] used by the American Airlines [[Sabre (computer system)|Sabre]] [[computer reservation system]]) for high-speed data access-and-update to customer information for their telephone operators (without waiting for overnight batch processing punch card systems).

When CICS was delivered to Amoco with Teletype Model 33 ASR support, it caused the entire OS/360 operating system to crash (including non-CICS application programs). The majority of the CICS Terminal Control Program (TCP{{snd}} the heart of CICS) and part of OS/360 had to be laboriously redesigned and rewritten by Amoco Production Company in Tulsa Oklahoma. It was then given back to IBM for free distribution to others.

In a few years,{{when|date=November 2012}} CICS generated over $60 billion in new hardware revenue for IBM, and became their most-successful mainframe software product.

In 1972, CICS was available in three versions{{snd}} DOS-ENTRY (program number 5736-XX6) for [[DOS/360 and successors|DOS/360]] machines with very limited memory, DOS-STANDARD (program number 5736-XX7), for DOS/360 machines with more memory, and OS-STANDARD V2 (program number 5734-XX7) for the larger machines which ran OS/360.<ref>{{cite book |url=http://bitsavers.org/pdf/ibm/370/CICS/GH20-1028-3_CICS_General_Information_Manual_Dec72.pdf |title=Customer Information Control System (CICS) General Information Manual |location=White Plains, New York |publisher=[[IBM]] |date=December 1972 |id=GH20-1028-3 |access-date=2016-04-01 |archive-date=2019-05-29 |archive-url=https://web.archive.org/web/20190529212532/http://bitsavers.org/pdf/ibm/370/CICS/GH20-1028-3_CICS_General_Information_Manual_Dec72.pdf |url-status=live }}</ref>

In early 1970, a number of the original developers, including Ben Riggins (the principal architect of the early releases) relocated to California and continued CICS development at IBM's [[Palo Alto, California|Palo Alto]] Development Center. IBM executives did not recognize value in software as a revenue-generating product until after federal law required software [[unbundling]]. In 1980, IBM executives failed to heed Ben Riggins' strong suggestions that IBM should provide their own [[EBCDIC]]-based operating system and integrated-circuit [[microprocessor]] chip for use in the [[IBM Personal Computer]] as a CICS [[thin client|intelligent terminal]] (instead of the incompatible Intel chip, and immature [[ASCII]]-based Microsoft 1980 [[DOS]]).

[[Image:Librarian listing of CICSGEN module.jpg|thumb|right|Beginning of a CICSGEN stage one module, 1982]]

Because of the limited capacity of even large processors of that era every CICS installation was required to assemble the source code for all of the CICS system modules after completing a process similar to [[system generation]] (sysgen), called ''CICSGEN'', to establish values for conditional assembly-language statements. This process allowed each customer to exclude support from CICS itself for any feature they did not intend to use, such as device support for terminal types not in use.

CICS owes its early popularity to its relatively efficient implementation when hardware was very expensive, its multi-threaded processing architecture, its relative simplicity for developing terminal-based real-time transaction applications, and many open-source customer contributions, including both debugging and feature enhancement.