For the daisy chain scheme of connecting I/O devices, which of the following statements is true?
A. It gives non-uniform priority to various devices
B. It gives uniform priority to all devices
C. It is only useful for connecting slow devices to a processor device
D. It requires a separate interrupt pin on the processor for each device
GATE 1996 · Computer Organization and Architecture · IO Handling · medium
Answer: A. It gives non-uniform priority to various devices — devices closer to the CPU in the daisy chain have higher interrupt priority.
Analyze the daisy chain mechanism: In a daisy chain scheme: (1) All devices share a single interrupt request (INT) line connected to the CPU. (2) When any device needs service, it asserts the shared INT line. (3) The CPU responds with an Interrupt Acknowledge (INTA) signal. (4) INTA propagates through the chain: it reaches Device 1 first. If Device 1 requested an interrupt, it captures INTA, places its vector on the data bus, and does not pass INTA further. If Device 1 did NOT request, it passes INTA to Device 2, and so on. (5) Devices earlier in the chain always have higher priority — this is non-uniform priority.
Evaluate each option: A. Non-uniform priority — CORRECT. Priority is determined by position in chain; Device 1 > Device 2 > Device 3. B. Uniform priority — INCORRECT. Priority is NOT uniform; position determines priority. C. Only for slow devices — INCORRECT. Daisy chain applies to any I/O device regardless of speed. D. Requires separate interrupt pin per device — INCORRECT. Only one shared INT line is used; no separate pins per device are needed (that describes a vectored interrupt controller with separate lines).