IBM's Cross-System Coupling Facility (XCF) allows authorized applications on one system to communicate with applications on the same system or on other systems. XCF transfers data and status information between members of a group that resides on one or more OS/390 or z/OS systems in a sysplex (SYStems comPLEX).

A sysplex is a set of software services and hardware components that allow OS/390 or z/OS systems to communicate and cooperate with each other to process customer work. For certain kinds of work, the sysplex provides parallel processing and improved data sharing.

A member is a specific function (one or more modules/routines) of a multisystem application that is defined to XCF and assigned to a group by the multisystem application. A member resides on one OS/390 or z/OS system in the sysplex and can use XCF services to communicate (send and receive data) with other members of the same group. Each Entire Net-Work node running the XCF line driver is identified as a different member in a group specifically set up for Entire Net-Work connectivity.

High-speed caching, list processing, and locking functions are provided by the sysplex hardware components. The coupling facility is a microprocessor unit that allows up to 32 OS/390 or z/OS systems to share data.

OS/390 or z/OS systems are directly connected to the coupling facilities through high bandwidth, high speed fiber optic links called coupling facility channels. Coupling facility channels provide a fast and efficient means for systems in the sysplex to access data in the coupling facility.

The coupling facility channel can use 50/125 multimode fiber at 531 megabits per second (Mbps), supporting a maximum distance of approximately one kilometer between the coupling facility and the processor.