GATE EC 2021 Set 1 — Question 42

MCQ+2 / -0.67EasyMachine Instructions & AddressingComputer OrganizationDigital Circuits

Digital Circuits → Computer Organization → Machine Instructions & Addressing

Last updated 5 September 2026

Question

The content of the registers are R1 = 25H, R2 = 30H and R3 = 40H. The following machine instructions are executed. PUSH{R1} PUSH{R2} PUSH{R3} POP{R1} POP{R2} POP{R3} After execution, the content of registers R1, R2, R3 are

Correct answer (A) R1 = 40H, R2 = 30H, R3 = 25H Solution Let's trace the stack operations: Initial register contents: R1 = 25H R2 = 30H R3 = 40H PUSH{R1} : R1's content (25H) is pushed onto the stack. Stack: [25H] PUSH{R2} : R2's content (30H) is pushed onto the stack. Stack: [25H, 30H] PUSH{R3} : R3's content (40H) is pushed onto the stack. Stack: [25H, 30H, 40H] Now, the POP operations occur in reverse order of PUSH (LIFO - Last In, First Out). POP{R1} : The top element of the stack (40H) is popped and loaded into R1. R1 = 40H Stack: [25H, 30H] POP{R2} : The new top element of the stack (30H) is popped and loaded into R2. R2 = 30H Stack: [25H] POP{R3} : The last element of the stack (25H) is popped and loaded into R3. R3 = 25H Stack: [] Final register contents: R1 = 40H R2 = 30H R3 = 25H This matches option (A). The final answer is oxed{ ext{R1 = 40H, R2 = 30H, R3 = 25H}} Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (A) R1 = 40H, R2 = 30H, R3 = 25H Solution Let's trace the stack operations: Initial register contents: R1 = 25H R2 = 30H R3 = 40H PUSH{R1} : R1's content (25H) is pushed onto the stack. Stack: [25H] PUSH{R2} : R2's content (30H) is pushed onto the stack. Stack: [25H, 30H] PUSH{R3} : R3's content (40H) is pushed onto the stack. Stack: [25H, 30H, 40H] Now, the POP operations occur in reverse order of PUSH (LIFO - Last In, First Out). POP{R1} : The top element of the stack (40H) is popped and loaded into R1. R1 = 40H Stack: [25H, 30H] POP{R2} : The new top element of the stack (30H) is popped and loaded into R2. R2 = 30H Stack: [25H] POP{R3} : The last element of the stack (25H) is popped and loaded into R3. R3 = 25H Stack: [] Final register contents: R1 = 40H R2 = 30H R3 = 25H This matches option (A). The final answer is oxed{ ext{R1 = 40H, R2 = 30H, R3 = 25H}}

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