Going all the way back to at least the IBM 7090, and presumably the 709, though I have not actually checked. The B5000 had IO processors as well.
On 7/14/2015 2:55 PM, William Donzelli wrote: >> ...I/O processors. > > I do not think you can claim that the 6600 I/O processors were all > that new. Many (most?) of the 1960s mainframes before the 6600 had > channel controllers. > > -- > Will >