||This article needs additional citations for verification. (May 2012)|
|Stable release||CICS Transaction Server 5.1 / October 3, 2012|
|Operating system||z/OS, z/VSE|
|Platform||IBM System z|
CICS is middleware designed to support rapid, high-volume online transaction processing. A CICS transaction is a unit of processing initiated by a single request that may affect one or more objects. This processing is usually interactive (screen-oriented), but background transactions are possible.
CICS provides services that extend or replace the functions of the operating system and are more efficient than the generalized services in the operating system and simpler for programmers to use, particularly with respect to communication with diverse terminal devices.
Applications developed for CICS may be written in a variety of languages and use CICS-supplied language extensions to interact with resources such as files, database connections, terminals, or to invoke functions such as web services. CICS manages the entire transaction such that if for any reason a part of the transaction fails all recoverable changes can be backed out.
While CICS has its highest profile among financial institutions such as banks and insurance companies, over 90 percent of Fortune 500 companies are reported to run CICS along with many government entities. CICS is also widely used by many smaller organizations. CICS is used in bank-teller applications, ATM systems, industrial production control systems, insurance applications, and many other types of interactive applications.
Recent CICS Transaction Server enhancements include support for Web services and Enterprise Java Beans (EJBs), Event processing, Atom feeds, and RESTful interfaces. CICS Transaction Server version 4.2, which became generally available on 24 June 2011, includes support for system events, 64-bit Java, transaction tracking, and password phrases.
CICS was preceded by an earlier, single threaded transaction processing system, IBM MTCS. An 'MTCS-CICS bridge' was later developed to allow these transactions to execute under CICS with no change to the original application programs.
CICS was originally developed in the United States at an IBM Development Center in Des Plaines, Illinois, beginning in 1966 to address requirements from the public utility industry. The first CICS product was released in 1968, named Public Utility Customer Information Control System, or PU-CICS. It became clear immediately that it had applicability to many other industries, so the Public Utility prefix was dropped with the introduction of the first release of the CICS Program Product on July 8, 1969, not long after IMS database management system.
In 1974, CICS development responsibility was shifted to IBM's Hursley, United Kingdom Laboratory, where development work continues today.
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 terminals were widely used later.
In the early days of IBM mainframes, computer software was free – 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 reservations system) for high-speed data access-and-update to customer information for their telephone operators (without waiting for over-night 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 - 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 short years[when?], CICS generated over $60 billion dollars in new hardware revenue for IBM, and became their most-successful mainframe software product.
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 Development Center. IBM executives did not recognize value in software as a revenue-generation 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 intelligent terminal (instead of the incompatible Intel chip, and immature ASCII-based Microsoft 1980 DOS).
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 system generation (sysgen) process 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.
Z notation 
Part of CICS was formalized using the Z notation in the 1980s and 1990s in collaboration with the Oxford University Computing Laboratory, under the leadership of Sir Tony Hoare. This work won a Queen's Award for Technological Achievement.
CICS and the World Wide Web 
CICS Transaction Server (TS) 2.1 introduced the capability for CICS transactions to be invoked via an HTTP request. This allowed CICS transactions to participate as servers in a POX or REST conversation.
CICS Transaction Server 2.3 added new EJB tracing capabilities, and new JCICS classes, allowing the invocation of CICS services using Java. End-to-end debugging was also introduced, making it easier to debug applications, from the Java client to the CICS application.
The Web services support in CICS Transaction Server Version 3.1 enables a CICS program to be a Web service provider or requester. CICS supports a number of industry standard and specifications including SOAP Version 1.1 and Version 1.2, Web services distributed transactions (WS-Atomic Transaction) and XML Encryption and Signing.
The input to DFHWS2LS is a set of control statements governing its processing and file containing WSDL for a web service to be accessed. The output is a set of language structures, each corresponding to a method in the WSDL, and a WSBIND file. This utility is intended for use by an application developer who wishes to access a web service as a client and has been provided its WSDL.
In this case, the application developer populates the language structure corresponding to the method they wish to invoke, writes the structure to the DFHWS-BODY CICS container, and executes the INVOKE WEBSERVICE Application Programming Interface (API). Execution of the API is synchronous, on return the DFHWS-BODY contains the response from the invoked web service mapped to a language structure.
The input to DFHLS2WS is a set of control statements governing its processing and file containing the language structure corresponding to the invocation parameters of a CICS application program. The output is the WSDL corresponding to the language structure, and a WSBIND file. This utility is intended for use by an application developer who wishes to expose a program's functionality as a web service.
In this case, the application program is invoked when an HTTP request for its services is received by the CICS region. The application program sees the request as language structure in either a CICS container or a COMMAREA (communication area), which one is governed by the control statements fed into DFHLS2WS. The application program performs its processing and writes the response back to the language structure it was invoked with.
In either case, whether the CICS application is acting as a web services client or server, the mapping of data to and from XML is governed by the generated WSBIND file. The message body is wrapped in, and unwrapped from, a SOAP envelope by CICS Web Services "plumbing" code external to the application program.
The connections between a web service, the WSBIND file, the WSDL, and the CICS transaction requesting or providing the service is done with CICS system level definitions and a configuration file.
CICS TS can be extended with additional programming features using SupportPacs. For example SupportPac CA8K introduces support for Atom feeds, and SupportPac CA1S adds support for the PHP scripting language, using the same Java-based PHP engine as Project Zero. Often SupportPac introduce new technologies into CICS before they are added into the main product, for example CA8K introduced Atom feeds before it was officially integrated into the product in CICS TS 4.1
CICS Family 
Although when CICS is mentioned, people usually mean CICS Transaction Server, the CICS Family refers to a portfolio of transaction servers, connectors (called CICS Transaction Gateway) and CICS Tools.
CICS on distributed platforms – not mainframes – is called IBM TXSeries, which is available on AIX, Windows, Solaris, and HP-UX operating systems. CICS is also available on other operating systems, notably IBM i and OS/2. The z/OS implementation (i.e., CICS Transaction Server for z/OS) is by far the most popular and significant.
Programming considerations 
Multiple-user interactive-transaction application programs were required to be quasi-reentrant in order to support multiple concurrent transaction threads. A software coding error in one application could block all users from the system. The modular design of CICS reentrant / reusable control programs meant that, with judicious "pruning," multiple users with multiple applications could be executed on a computer with just 32K of expensive magnetic core physical memory (including the operating system).
Considerable effort was required by CICS application programmers to make their transactions as efficient as possible. A common technique was to limit the size of individual programs to no more than 4,096 bytes, or 4K, so that CICS could easily reuse the memory occupied by any program not currently in use for another program or other application storage needs. When virtual memory was added to versions OS/360 in 1972, the 4K strategy became even more important to reduce paging and thrashing unproductive resource-contention overhead.
The efficiency of compiled high-level COBOL and PL/I language programs left much to be desired. Many CICS application programs continued to be written in assembler language, even after COBOL and PL/I support became available.
With 1960s-and-1970s hardware resources expensive and scarce, a competitive "game" developed among system optimization analysts. When critical path code was identified, a code snippet was passed around from one analyst to another. Each person had to either (a) reduce the number of bytes of code required, or (b) reduce the number of CPU cycles required. Younger analysts learned from what more-experienced mentors did. Eventually, when no one could do (a) or (b), the code was considered optimized, and they moved on to other snippets. Small shops with only one analyst learned CICS optimization very slowly (or not at all).
Unfortunately, many of the "rules" were frequently broken, especially by COBOL programmers who might not understand the internals of their programs or fail to use the necessary restrictive compile time options. This resulted in "non-re-entrant" code that was often unreliable, leading to spurious storage violations and entire CICS system crashes.
The entire partition, or Multiple Virtual Storage (MVS) region, operated with the same memory protection key including the CICS kernel code. Program corruption and CICS control block corruption was a frequent cause of system downtime. A software error in one application program could overwrite the memory (code or data) of one or all currently running application transactions. Locating the offending application code for complex transient timing errors could be a very-difficult operating-system analyst problem.
These serious shortcomings persisted for multiple new releases of CICS over a period of more than 20 years. CICS application transactions were often mission-critical for public utility companies, large banks and other multi-billion-dollar financial institutions. Top-quality CICS skills were in high demand and short supply. The complex learning curve was shallow and long. Unqualified novice developers could have a major negative impact on company operations.
Eventually, it became possible to provide a measure of advance application protection by performing all testing under control of a monitoring program that also served to provide Test and Debug features. One such software offering was known as OLIVER, which prevented application programs corrupting memory by using instruction set simulation of the application code, providing partial virtualization.
Macro-level programming 
When CICS was first released, it only supported application transaction programs written in IBM 360 Assembler. COBOL and PL/I support were added years later. Because of the initial assembler orientation, requests for CICS services were made using assembler language macros. For example the request to read a record from a file were made by a macro call to the "File Control Program" of CICS might look like this:
This gave rise to the later terminology "Macro-level CICS."
When high-level language support was added, the macros were retained and the code was converted by a pre-compiler that expanded the macros to their COBOL or PL/I CALL statement equivalents. Thus preparing a HLL application was effectively a "two-stage" compile — output from the preprocessor fed into the HLL compiler as input.
Command-level programming 
During the 1980s, IBM at Hursley produced a "half-way house" version of CICS that supported what became known as "Command-level CICS." This release still supported the older programs but introduced a new layer of execution to the new Command level application programs.
A typical Command-level call might look like the following:
EXEC CICS SEND MAPSET(MPS1) MAP(MP1) END-EXEC.
This is pre-processed by a pre-compile batch translation stage, which converts the embedded commands (EXECs) into call statements to a stub subroutine. So, preparing application programs for later execution still required two stages. It was possible to write "Mixed mode" applications using both Macro-level and Command-level statements.
At execution time, the command-level commands were converted back using a run-time translator, "The EXEC Interface Program", to the old Macro-level call, which was then executed by the mostly unchanged CICS nucleus programs.
Run-time conversion 
The Command-level-only CICS introduced in the early 1990s offered some advantages over earlier versions of CICS. However, IBM also dropped support for Macro-level application programs written for earlier versions. This meant that many application programs had to be converted or completely rewritten to use Command-level EXEC commands only.
By this time, there were perhaps millions of programs worldwide that had been in production for decades in many cases. Rewriting them inevitably introduced new bugs without necessarily adding new features.
It was, however, possible to execute old Macro-level programs using conversion software such as APT International's Command CICS. This allowed applications to take advantage of the new features of later versions of CICS while, at the same time, retaining the original unaltered code base. It is believed that there are still programs running today using this same technology.
New programming styles 
Recent CICS Transaction Server enhancements include support for a number of modern programming styles.
CICS Transaction Server Version 2.1 introduced support for Enterprise Java Beans (EJB). CICS Transaction Server Version 2.2 supported the Software Developers Toolkit. CICS provides the same run-time container as IBM's WebSphere product family so EJB applications are portable between CICS and Websphere and there is common tooling for the development and deployment of EJB applications.
A CICS transaction is a set of operations that perform a task together. Usually, the majority of transactions are relatively simple tasks such as requesting an inventory list or entering a debit or credit to an account. A primary characteristic of a transaction is that it should be atomic. On IBM System z servers, CICS easily supports thousands of transactions per second, making it a mainstay of enterprise computing.
CICS applications comprise transactions, which can be written in numerous programming languages, including COBOL, PL/I, C, C++, IBM Basic assembly language, REXX, and Java.
Each CICS program is initiated using a transaction identifier. CICS screens are usually sent as a construct called a map, a module created with Basic Mapping Support (BMS) assembler macros or third-party tools. CICS screens may contain text that is highlighted, has different colors, and/or blinks depending on the terminal type used. An example of how a map can be sent through COBOL is given below. The end user inputs data, which is made accessible to the program by receiving a map from CICS.
EXEC CICS SEND MAPSET(MPS1) MAP(MP1) END-EXEC.
Example of BMS Map Code 
Basic Mapping Support defines the screen format through assembler macros such as the following. This was assembled to generate both the physical map set – a load module in a CICS load library – and a symbolic map set – a structure definition or DSECT in PL/I, COBOL, assembler, etc. which was copied into the source program.
LOSMATT DFHMSD TYPE=MAP, X MODE=INOUT, X TIOAPFX=YES, X TERM=3270-2, X LANG=COBOL, X MAPATTS=(COLOR,HILIGHT), X DSATTS=(COLOR,HILIGHT), X STORAGE=AUTO, X CTRL=(FREEKB,FRSET) * LOSATT DFHMDI SIZE=(24,80), X LINE=1, X COLUMN=1 * LSSTDII DFHMDF POS=(1,01), X LENGTH=04, X COLOR=BLUE, X INITIAL='MQCM', X ATTRB=PROT * DFHMDF POS=(24,01), X LENGTH=79, X COLOR=BLUE X ATTRB=ASKIP, X INITIAL='PF7- 8- 9- 10- X 11- 12-CANCEL' * DFHMSD TYPE=FINAL END
In the z/OS environment, a CICS installation comprises one or more regions (generally referred to as a "CICS Region") , spread across one or more z/OS system images. Although it processes interactive transactions, each CICS region may be started as a batch processing|batch address space with standard JCL statements: it's a job that runs indefinitely. Alternatively, each CICS region may be started as a started task. Whether a batch job or a started task, CICS regions may run for days, weeks, or even months before shutting down for maintenance (MVS or CICS).
Installations are divided into multiple address spaces for a wide variety of reasons, such as:
- application separation,
- function separation,
- avoiding the workload capacity limitations of a single region, or address space.
A typical installation consists of a number of distinct applications. Each application usually has its own "Terminal-Owning Region" (TOR) and one or more "Application-Owning Regions" (AORs), though other topologies are possible. For example, the AORs might not perform File I/O. Instead there would be "File-Owning Regions" (FORs) that performed the File I/O on behalf of transactions in the AOR.
Each CICS region comprises one major task on which every transaction runs, although certain services such as access to DB2 data use other tasks (TCBs). Within a region transactions are cooperatively multitasked — they are expected to be well-behaved and yield the CPU rather than wait. CICS services handle this automatically.
Each unique CICS "Task" or transaction is allocated its own dynamic memory at start-up and subsequent requests for additional memory were handled by a call to the "Storage Control program" (part of the CICS nucleus or "kernel"), which is analogous to an operating system.
A CICS system consiste of the online nucleus, batch support programs, and applications services.
the CICS nucleus consists of a number of functional modules.
- Task Control Program (KCP).
- Storage Control Program (SCP).
- Program Control Program (PCP).
- Program Interrupt Control Program (PIP).
- Interval Control Program (ICP).
- Dump Control Program (DCP).
- Terminal Control Program (TCP).
- File Control Program (FCP).
- Transient Data Control Program (TDP).
- Temporary Storage Control Program (TSP).
Support programs 
In addition to the online functions CICS had several support programs that ran as batch jobs. :pp.34-35
- High level language (macro) preprocessor.
- Command language translator.
- Dump utility – prints formatted dumps generated by CICS Dump Management.
- Trace utility – formats and prints CICS trace output.
- Journal formatting utility – prints a formatted dump of the CICS region in case of error.
Applications services 
The following components of CICS support application development.:pp.35-37
- Basic Mapping Support (BMS) provides device-independent terminal input and output.
- Data Interchange Program (DIP) provides support for IBM 3770 and IBM 3790 programmable devices.
- 2260 Compatibility allows programs written for IBM 2260 display devices to run on 3270 displays.
- EXEC Interface Program – the stub program that converts calls generated by
EXEC CICScommands to calls to CICS functions.
- Built-in Functions – table search, phonetic conversion, field verify, field edit, bit checking, input formatting, weighted retrieval.
Different countries have differing pronunciations 
- Within IBM (specifically Tivoli) it is referred to as //.
- In the US, it is more usually pronounced by reciting each letter //.
- In Australia, Belgium, Canada, Hong Kong, the UK and some other countries, it is pronounced //.
- In Finland, it is pronounced [kiks]
- In France, it is pronounced [se.i.se.ɛs].
- In Germany, Austria and Hungary, it is pronounced [ˈtsɪks] and, less often, [ˈkɪks].
- In India, it is pronounced kicks.
- In Italian, is pronounced [ˈtʃiks].
- In Poland, it is pronounced [ˈkʲiks].
- In Portugal and Brazil, it is pronounced [ˈsiks].
- In Russia, it is pronounced kiks.
- In Slovenia, it is pronounced kiks.
- In Spanish, it is pronounced [ˈθiks].
- In Israel, it is pronounced kicks.
- In Uganda, it is pronounced kicks.
- In Turkiye, it is pronounced kiks.
See also 
- IBM TXSeries (CICS on distributed platforms)
- IBM WebSphere
- IBM 2741
- IBM 2260
- IBM 3270
- IBM OD390
- OS 360
- IBM Corporation. "CICS Transaction Server for z/OS, Version 3.2 Glossary:T". Retrieved December 7, 2012.
- IBM, 2004. CICS 35 year anniversary
- IBM, 2011. CICS Transaction Server for z/OS V4.2
- King, Steve (1993). "The Use of Z in the Restructure of IBM CICS". In Hayes, Ian. Specification Case Studies (2nd ed.). New York: Prentice Hall. pp. 202–213. ISBN 0-13-832544-8.
- IBM, 2010, CICS TS 4.1 Information Centre, http://publib.boulder.ibm.com/infocenter/cicsts/v4r1/index.jsp?topic=/com.ibm.cics.ts.webservices.doc/concepts/dfhws_standards.html
- IBM Corporation. "Basic mapping support". CICS Information Center.
- IBM (September 13, 2010). "CICS Transaction Server glossary". CICS Transaction Server for z/OS V3.2. IBM Information Center, Boulder, Colorado. Retrieved 12 December 2010.
- IBM Corporation (1975). Customer Information Control System (CICS) System Programmer's Reference Manual.
- IBM Corporation (1977). Customer Information Control System/Virtual Storage (CICS/VS) Version 1, Release 3 Introduction to Program Logic Manual.
- IBM, 2004, CICS an introduction, ftp://service.boulder.ibm.com/software/htp/cics/PDF/cics_introduction.pdf
- IBM CICS Family official website
- IBM CICS Whitepaper - Why to choose CICS Transaction Server for new IT projects
- CICS official 35th Anniversary website
- CICS User Community website for CICS related news, announcements and discussions
- Bob Yelavich's CICS focused website. (Archived copy from 5 Feb 2005) Note that this site uses frames, but on high-resolution screens the left-hand frame, which contains the site index, may be hidden. Scroll right within the frame to see its content.