A sysplex (systems complex) is the set of one or more MVS™ systems that is given an XCF sysplex name and in which the authorized programs in the systems can then use XCF services. XCF services are available in both single and multisystem environments. A multisystem environment is defined as two or more MVS systems residing on one or more processors. In either environment, as you proceed to design your multisystem application, you need to communicate with the system programmer in your installation about the resources you will need. See Providing Information to Your System Programmer for more information. System programmers should consult z/OS MVS Setting Up a Sysplex for complete information on initializing and managing MVS systems in a sysplex.

A group is the set of related members defined to XCF by a multisystem application in which members of the group can communicate (send and receive data) between MVS systems with other members of the same group. A group can span one or more of the systems in a sysplex and represents a complete logical entity to XCF.

You can set up a multisystem application as more than one group, but the logical entity for XCF is the group.

A member is a specific function (one or more routines) of a multisystem application that is defined to XCF and assigned to a group by the multisystem application. A member resides on one system in the sysplex and can use XCF services to communicate (send and receive data) with other members of the same group. However, a member is not a particular task and is not a particular routine. The member concept applies to all authorized routines running in the address space in which the member was defined. The entire address space has the ability to act as that member. All tasks and SRBs in that address space can request services on behalf of the member.

When you define a member, it is associated with the address space in which the IXCJOIN was issued. The member always ends when the address space ends or when the system ends. If you want the member's existence tied to a more specific unit of work, you can further associate the member with either the task or job step task in which the IXCJOIN was issued. In this case, the member also ends when the associated task (or job step task, if selected) ends. This is explained in more detail in the the topics entitled Member Association and Member Termination.

Members of XCF groups are unique within the sysplex. However, XCF allows you to define more than one member from the same task or address space, and have those members belong to different XCF groups. You might use this option if the number of members you require exceeds the maximum (XCF allows up to 2047 members in a group), and you must define another group. You should be aware, however, that designing a multisystem application with a very large number of members has an associated cost to the system in terms of processor storage.