The IBM Virtual Machine Communication Facility (VMCF) is a feature of the VM/370 operating system introduced in Release 3 in 1976.
It "provides a method of communication and data transfer between virtual machines operating under the same VM/370 system.
"[1] VMCF uses paravirtualization through the diagnose instruction VMCF SEND function to send data, in blocks of up to 2048 bytes, from one virtual machine to another.
It provides a simpler interface and greater performance than the prior use of virtual channel-to-channel adapters for the same purpose.
[2] VMCF was superseded by the Inter User Communication Vehicle (IUCV), introduced in 1980 with VM/SP.