Complex sentence: The PC/AT-bus is a 16-bit (or 80286 -) version of the PC/XT bus was introduced with the IBM PC/AT, officially termed "I/O Channel" by IBM.
Split into simpler sentences: The PC/AT-bus, a 16-bit (or 80286 -) version of the PC/XT bus, was introduced with the IBM PC/AT. This bus was officially termed "I/O Channel" by IBM.