Suppose a processor does not have any stack pointer register.

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Suppose a processor does not have any stack pointer register. Which of the following statements is true?

1. It cannot have subroutine CALL instruction
2. It can have subroutine CALL instruction, but no nested subroutine CALLS
3. Nested subroutine CALLS are possible, but interrupts are not
4. All sequences of subroutine CALLS and also interrupts are possible

Correct Option: A

Stack pointer register holds the address of top of stack, which is the location of memory at which the CPU should resume its execution after servicing some interrupt or subroutine call. So if SP register not available then no subroutine call instructions are possible.
Hence (a) is correct option.