This is a special type of z/VM® service machine that runs the Coupling Facility Control Code (CFCC). This code is not part of z/VM and is loaded directly from the processor. Because z/VM is executing the actual code that runs in a real coupling facility, there is basically no difference in function between a real coupling facility and z/VM's implementation.

The system administrator must define a user ID for each CF Service Machine that will run under z/VM. To define each user ID as a CF Service Machine, the CFVM operand must be specified on the OPTION directory control statement of each CF Service Machine. The CFVM operand defines the virtual machine as a CF Service Machine and allow connections between itself and coupled guests.

You can define up to eight CF Service Machines. Up to 32 coupled guests can be connected to each CF Service Machine. When the processor and z/VM are so capable, each CF Service Machine can couple to up to seven other CF Service Machines.