Channel-to-channel adapter

In IBM mainframe technology, a channel-to-channel adapter (CTCA)^{[1][2] [3]} is a device that connects two input/output channels on (usually) two separate computer systems.^[4]

The adapter allows one computer system to be treated as an input/output device by another. It is used "to link the processing units in a loosely coupled multiprocessing system.^[5]

Virtual channel-to-channel adapters (VCTCA) are often used to communicate between two virtual machines in the z/VM operating system. The Virtual Machine Communication Facility (VMCF), and later Inter User Communication Vehicle (IUCV) are now often used in place of VCTCAs because they provide a simpler interface and improved performance.^[6]

On IBM z processors, the functionality of a CTCA is implemented by connecting two ESCON channels or two FICON channels either point-to-point or via a director.^[7]