By the time the S/360 was announced, IBM had already been producing top-of-the-line systems with the main processor sharing memory with several I/O "channels" f

By the time the S/360 was announced, IBM had already been producing top-of-the-line systems with the main processor sharing memory with several I/O "channels" for several years -- which would be "mainframes" by any reasonable definition I can think of other than "S/360 and derivatives" (which, by the way, excludes competing mainframe systems from Univac and Burroughs, among others).