GATE CSE 1995 | Question: 1.2

Question

Which of the following statements is true?

• A. ROM is a Read/Write memory

• B. PC points to the last instruction that was executed

• C. Stack works on the principle of LIFO

• D. All instructions affect the flags

Comments

MOV: Does not affect any flags

PUSH/POP: Do not affect flags typically

JMP: Does not affect flags

CALL/RET: Do not affect flags

 

Answer 1

It is (C).

Only the top of the stack can be accessed at any time. You can imagine a stack to be opened from only one side data structure. So that if we put one thing over the other, we are able to access the last thing we inserted first. That is Last in First Out (LIFO).

• ROM is Read-Only Memory.
• PC points to the next instruction to be executed.
• Not all instructions affect the flags.

Comments

eg for 4th option is push pop instruction  does not affect flag status

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Simple LOAD or STORE instructions don't need ALU cycle to execute and so they willnot affect flags like OVERFLOW,CARRY,ZERO,SIGN ...

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https://gateoverflow.in/85391/gate1990-4-iii

@vickyrix draw some light on this question

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for option D)

conditional CALL or JUMP instructions don't affect any flags : https://gateoverflow.in/85391/gate-cse-1990-question-4-iii?show=497018#a497018

Answer 2

option 1:--> False , Because Rom is read only memory.

option 2--> False , because PC Store Next instruction Address .

option 3--> True , Because Stack work on LIFO principle

option 3--> Flase ,Because not all instruction required flags , Example :--push,pop,load,store etc

Answer 3

Ans: C

Comments

Please give explanation also, that will be more helpful.