Customer Information Control System (CICS) is a transaction server that runs primarily on IBM mainframe systems under z/OS and z/VSE.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 programming 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 June 24, 2011, includes support for system events, 64-bit Java, transaction tracking, and password phrases.