The IBM 2821 Control Unit was used to attach card readers, card punches and line printers to the IBM System/360 and IBM System/370 families of computers. The devices attached were as follows:
The IBM 2540 card reader and card punch;
The IBM 1403 models 2, 3, 7 and N1 line printer; and
The IBM 1404 model 2 line printer and card reader.
Six models of the IBM 2821 Control Unit were available, as follows:
Model 1 attached one IBM 2540 and one IBM 1403;
Model 2 attached one IBM 1403;
Model 3 attached two or three IBM 1403s;
Model 4 attached one IBM 2540 and one IBM 1404, but only on IBM System/360 models 30, 40 and 50;
Model 5 attached one IBM 2540 and two or three IBM 1403s; and
Model 6 attached one IBM 2540.
