TEST SUBCHANNEL ) we use this as the ID of the device we wish to talk to, the most
important of these instructions are START SUBCHANNEL ( to start IO ), TEST SUBCHANNEL ( to check
whether the IO completed successfully ), & HALT SUBCHANNEL ( to kill IO ), a subchannel
TEST SUBCHANNEL ) we use this as the ID of the device we wish to talk to, the most
important of these instructions are START SUBCHANNEL ( to start IO ), TEST SUBCHANNEL ( to check
whether the IO completed successfully ), & HALT SUBCHANNEL ( to kill IO ), a subchannel