The device driver subprogram relays the information to the background process by calling the background program at {HEAD ~ an entry point} which is made available to {TAIL ~ the device driver} at a predetermined interrupt vector location, enabling the device driver to pass the memory address of the foreground storage area, together with the size of the block of information to be communicated, to the background program 
The device driver subprogram relays the information to the background process by calling the background program at { HEAD ~ an entry point } which is made available to { TAIL ~ the device driver } at a predetermined interrupt vector location , enabling the device driver to pass the memory address of the foreground storage area , together with the size of the block of information to be communicated , to the background program
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH