Data Byte Counting in I/O Channels
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
In the contemporary data processing system illustrated in Fig. 1, one or more groups of I/O channels 1 operate through common processors 2, termed directors, for exchanging input and output information between a host central system 3 and channel-to-control unit I/O interfaces 4 associated with the channels. The channels in each group receive service from the associated director in a predetermined order of priority. If a director is unavailable when a device or control unit requests service through as associated channel the process in that channel may overrun (refer to "IBM System/370 Principles of Operation," form GA22-7000-5, August 1976, page 220). Overruns impose costly programming overhead on the host system, for diagnosing the cause of the overrun and reinitiating the input or output process interrupted by the overrun.