CICS (Customer Information Control System) is an online transaction processing (OLTP) program from IBM that, together with the COBOL programming language, has formed over the past several decades the most common set of tools for building customer transaction applications in the world of large enterprise mainframe computing. A great number of the legacy applications still in use are COBOL/CICS applications. Using the application programming interface (API) provided by CICS, a programmer can write programs that communicate with online users and read from or write to customer and other records (orders, inventory figures, customer data, and so forth) in a database (usually referred to as "data sets") using CICS facilities rather than IBM's access methods directly. Like other transaction managers, CICS can ensure that transactions are completed and, if not, undo partly completed transactions so that the integrity of data records is maintained.
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IBM markets or supports a CICS product for OS/390, Unix, and Intel PC operating systems. Some of IBM's customers use IBM's Transaction Server to handle e-business transactions from Internet users and forward these to a mainframe server that accesses an existing CICS order and inventory database.
CICS was not the first Transaction Processing Monitor (TPM), that honour falls to the predecessors of TPF in the airline industry. The production of CICS was influenced by these early TPM such as the SABRE project. CICS is the work of many people, but like all things started with one, Ben Riggins. Riggins saw that the many opportunities that things like the SABRE project had brought to the Airline industry could equally well be applied to the Public Utility market in the United States. PUCICS (Public Utility Customer Information Control System) was basically written to fulfill that need. CICS, as it eventually became know, first saw the light of day as a free program in 1968, although you did need to have bought one of those new, powerful 32 bit IBM 360s. It is written in assembler and was really only a terminal control program with some database capability. CICS eventually goes through several versions picking up more and more of the attributes of a TPM along the way (for example elementary Transaction Control by the early 70's).
By 1979 it was realised that the assembler based CICS with its poor multi-threaded single memory model could not continue into future, and a new CICS, the basis of the current Mainframe version, was written in a high level language. This rework was so extensive that it was incorporated gradually and it was not until the late 80's that it was finally complete when version 3 was introduced. In the early 90's the CICS Application Programming Interface was extended to the AS400 and OS/2 platforms, with the Encina Tool Kit version being announced on AIX, IBM's UNIX like operating system in 1992.
