Consider the following two statements about interrupt handling mechanisms in a CPU.
S1: In non-vectored interrupt mechanism, it usually takes more time to start the Interrupt Service Routine (ISR) when compared to that in a vectored interrupt mechanism.
S2: In daisy-chain interrupt mechanism, the CPU polls all the input devices individually to determine the source of the interrupt.
Which one of the following options is correct with respect to S1 and S2?

Question

A database has 25,000 fixed-length records of 100 bytes (primary key 15 bytes). The data file is block-aligned so each record is fully contained within a block. The file is indexed by a primary index file, also block-aligned and ordered. Block size is 1024 bytes and a block pointer is 5 bytes. Each index entry stores the block’s anchor key (15 bytes) and a pointer (5 bytes). Binary search on an index file of \(b\) blocks needs \(\lceil \log_2 b \rceil\) block accesses in the worst case. Given a key, the number of block accesses required to identify the data file block that may contain the record, in the worst case, is ____________.

Answer 1

This question checks two separate ideas: how fast a CPU can reach the correct ISR under vectored versus non-vectored interrupts, and how the daisy-chain scheme actually finds which device raised the interrupt.

On S1 (vectored vs non-vectored speed): A vectored interrupt hands the CPU the ISR's starting address directly during the interrupt acknowledge cycle, so execution jumps to the ISR almost instantly. A non-vectored interrupt gives no such address; the CPU must first run a short identification routine, often polling each device's status flag, to work out which device interrupted, and only then branch to that device's ISR. This extra identification step is real overhead, so non-vectored handling is slower to start the ISR. S1 is correct.
On S2 (how daisy chaining finds the source): Daisy chaining wires every interrupting device in series on one shared request and acknowledge line. When the CPU sends the acknowledge signal, it ripples down the chain in hardware, device by device, until it reaches the first device that is actually asking for service; that device grabs the signal and identifies itself, and the CPU never has to interrogate the devices in software. This is the opposite of polling. S2 is incorrect.

Since S1 is true and S2 is false, the correct choice is the option that states exactly that.

Let's summarize:

Vectored interrupts are faster to reach the ISR because the device supplies its own vector address; non-vectored interrupts need an extra software identification step.
Daisy chaining finds the interrupting device through a hardware acknowledge chain, not through CPU-driven polling of each device.

So the answer is option (C): S1 is true and S2 is false.

Answer 2

This question checks two separate ideas: how fast a CPU can reach the correct ISR under vectored versus non-vectored interrupts, and how the daisy-chain scheme actually finds which device raised the interrupt.

On S1 (vectored vs non-vectored speed): A vectored interrupt hands the CPU the ISR's starting address directly during the interrupt acknowledge cycle, so execution jumps to the ISR almost instantly. A non-vectored interrupt gives no such address; the CPU must first run a short identification routine, often polling each device's status flag, to work out which device interrupted, and only then branch to that device's ISR. This extra identification step is real overhead, so non-vectored handling is slower to start the ISR. S1 is correct.
On S2 (how daisy chaining finds the source): Daisy chaining wires every interrupting device in series on one shared request and acknowledge line. When the CPU sends the acknowledge signal, it ripples down the chain in hardware, device by device, until it reaches the first device that is actually asking for service; that device grabs the signal and identifies itself, and the CPU never has to interrogate the devices in software. This is the opposite of polling. S2 is incorrect.

Since S1 is true and S2 is false, the correct choice is the option that states exactly that.

Let's summarize:

Vectored interrupts are faster to reach the ISR because the device supplies its own vector address; non-vectored interrupts need an extra software identification step.
Daisy chaining finds the interrupting device through a hardware acknowledge chain, not through CPU-driven polling of each device.

So the answer is option (C): S1 is true and S2 is false.

Show Hint

The Correct Option is C

Solution and Explanation

Questions Asked in GATE CS exam