Virtual Labs

Correlating Branch Prediction with Two-Level Predictors

What is the primary function of a branch instruction in a program?

a: To perform arithmetic calculations. Explanation

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b: To change the flow of execution to a different part of the code. Explanation

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c: To load data from memory. Explanation

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d: To store data in a register. Explanation

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What does 'BNE' typically stand for in assembly language?

a: Branch if Negative Explanation

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b: Branch if Not Equal Explanation

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c: Buffer Not Empty Explanation

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d: Branch if Equal Explanation

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What is the main goal of branch prediction?

a: To reduce the program's memory usage. Explanation

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b: To make the CPU run at a higher clock speed. Explanation

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c: To prevent the instruction pipeline from stalling. Explanation

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d: To simplify the instruction set. Explanation

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A simple 1-bit branch predictor stores which of the following?

a: The target address of the branch. Explanation

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b: The last outcome of the branch (Taken or Not Taken). Explanation

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c: A 2-bit saturating counter. Explanation

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d: The instruction opcode. Explanation

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What are the four states of a 2-bit saturating counter in a branch predictor?

a: Taken, Not Taken, Maybe Taken, Maybe Not Taken Explanation

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b: Start, Wait, Execute, End Explanation

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c: 0, 1, 2, 3 Explanation

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d: Strongly Not Taken, Weakly Not Taken, Weakly Taken, Strongly Taken Explanation

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What is the main advantage of a 2-bit predictor over a 1-bit predictor?

a: It is cheaper to implement in hardware. Explanation

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b: It is faster at making a prediction. Explanation

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c: It is more tolerant of a single different outcome in a sequence. Explanation

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d: It can predict the branch target address. Explanation

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For a 2-bit predictor, how many consecutive mispredictions does it take to change a prediction from 'Taken' (from state 11) to 'Not Taken'?

a: 1 Explanation

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b: 2 Explanation

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c: 3 Explanation

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d: 4 Explanation

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A simple branch predictor (like 1-bit or 2-bit) will perform poorly on which branch outcome pattern?

a: T, T, T, T, T, N Explanation

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b: N, N, N, N, N, N Explanation

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c: T, N, T, N, T, N Explanation

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d: T, T, T, T, T, T Explanation

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A 'pipeline flush' or 'stall' due to a branch misprediction means what?

a: The CPU must clear the pipeline of incorrectly fetched instructions and restart from the correct branch path. Explanation

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b: The CPU has run out of memory and must write pipeline contents to disk. Explanation

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c: The CPU's cooling system is flushing the pipeline with coolant. Explanation

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d: The pipeline is full and is operating at maximum efficiency. Explanation

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