Also known as Micro Channel Architecture (MCA), it was an earlier, proprietary 32-bit bus from IBM used in PS/2, RS/6000 and certain ES/9370 models. Micro Channel cards contained a unique ID that eliminated the error-prone task of setting DIP switches on ISA cards, the primary peripheral expansion of the era. MCA supported 15 levels of bus mastering and transferred data from 20 to 80MBytes/sec. In late 1996, IBM discontinued its use in favor of PCI. See PC data buses and PCI.