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.
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.
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