Three devices, A, B, and C, are connected to the bus of a computer. I/O transfers for all three devices use interrupt control. Interrupt nesting for devices A and B is not allowed, but interrupt requests from C may be accepted while either A or B is being serviced. Suggest different ways in which this can be accomplished in each of the following cases:

(a) The computer has one interrupt-request' line.

(b) Two interrupt-request lines, INTR1 and INTR2, are available, with INTR1 having higher priority. Specify when and how interrupts are enabled and disabled in each case.