The hardware and software that turns an IBM mainframe Base Sysplex system into a Parallel Sysplex. It is made up of special microcode built into the machine, and the CFCC operating system (Coupling Facility Control Code). It can be implemented as a stand-alone machine, in an LPAR logical partition or in a spare processor that becomes an Internal Coupling Facility (ICF).
The Coupling Facility allows up to 32 coupled systems to communicate using three coupling structures: "list" for simple data, "cache" for data buffering and "lock" for control of access to ensure data integrity. See Parallel Sysplex