channel-to-channel adapter
In IBM mainframe technology, a channel-to-channel adapter (CTCA){{cite manual
| title = IBM System/370 Special Feature Description: Channel-to-Channel Adapter
| id = GA22.6983·Q
| date = March 1972
| edition = First
| url = http://bitsavers.org/pdf/ibm/370/CTCA/GA22-6983-0_Special_Feature_Description_Channel-to-Channel_Adapter_Mar72.pdf
| publisher = IBM
}}
| title = Enterprise Systems Architecture/390 Channel-to-Channel Adapter for the System/360 and System/370 I/O Interface
| id = SA22-7091-01
| edition = 2nd
| date = October 1991
| publisher = International Business Machines Corporation
}}
| title = Enterprise Systems Architecture/390 ESCON Channel-to-Channel Adapter
| id = SA22-7203-00
| edition = 1st
| date = October 1990
| publisher = International Business Machines Corporation
}}
is a device that connects two input/output channels on (usually) two separate computer systems.{{cite book|last=IBM Corporation|title=IBM System/360 Model 65 Functional Characteristics|year=1968|page=10|url=http://www.bitsavers.org/pdf/ibm/360/functional_characteristics/A22-6884-3_360-65_funcChar.pdf|id=A22-6884-3}}
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.{{cite web|last=IBM Corporation|title=System/370 Model 158|url=http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3158.html|archive-url=https://web.archive.org/web/20050311003135/http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3158.html|url-status=dead|archive-date=March 11, 2005|work=IBM Archives|date=23 January 2003 |accessdate=January 7, 2014}}
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.{{cite journal |last1=Jensen |first1=R.M. |title=A formal approach for communication between logically isolated virtual machines |journal=IBM Systems Journal |date=1979 |volume=18 |issue=1 |pages=71–92 |citeseerx=10.1.1.91.1907 |doi=10.1147/sj.181.0071 }}
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.{{cite book
| title = ESCON and FICON Channel-to-Channel Reference
| id = SB10-7034-05
| year = 2011
| url = https://www.ibm.com/support/pages/sites/default/files/inline-files/SB10-7034-05.pdf
| series = System z
| publisher = IBM
| access-date = May 30, 2025
}}