Micro Channel architecture

The Micro Channel architecture (usually MCA, although not officially) was an I/O bus designed by IBM which replaced the ISA bus used on IBM PCs, and was used on IBM PS/2s.

It was synchronous, and 32 bits wide (although a 16-bit mode was available for low-cost implementation on low-performance cards).

It was intended (IBM hoped) to also become the standard bus for IBM-compatible PCs, and was used on a few non-IBM machines. It did not really catch on, however (in part due to IBM's licensing fees), and the main replacement for ISA turned out to be the PCI bus.