The only thing not mentioned are the co-processors that handle a lot of ancillary tasks and thus keep the main CPUs free for more work. For instance, printing a

The only thing not mentioned are the co-processors that handle a lot of ancillary tasks and thus keep the main CPUs free for more work. For instance, printing a report might require just 1 interrupt per page, the rest being handled by the printing controller. The TN3270 terminals talk to a separate communications controller before being passed to the cpu, and the disks used to be able to return results in a sorted order, not sure what they do now...