Mainframes aren't hotbeds of compute power - they are all about the I/O. Your typical COBOL program reads a record, does some moderate processing, and writes a

Mainframes aren't hotbeds of compute power - they are all about the I/O. Your typical COBOL program reads a record, does some moderate processing, and writes a record out. Over and over. So keeping the input and output channels full so processing wouldn't stall was a key design goal.