The device driver subprogram relays the information to the background process by calling the background program at an entry point which is made available to the device driver at {HEAD ~ a predetermined interrupt vector location}, enabling {TAIL ~ 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 
enabling
The device driver subprogram relays the information to the background process by calling the background program at an entry point which is made available to the device driver at { HEAD ~ a predetermined interrupt vector location } , enabling { TAIL ~ 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
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