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Questions and Answers
What is the first stage of pipelining, where the CPU retrieves an instruction from memory?
Fetch Instruction (FI)
What is the purpose of the Calculate Operands (CO) stage in pipelining?
To calculate the effective address of the operands if required
What is the primary function of the Decode Instruction (DI) stage in pipelining?
To decode the fetched instruction and determine the operation and operands needed
What is the final stage of pipelining, where the results of the execution are stored?
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What is the benefit of using a pipeline architecture in computer organization?
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What is a conditional branch instruction in computer programming?
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What is the main difference between an unconditional branch and a conditional branch?
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What is the purpose of the Execute Instructions (EI) stage in pipelining?
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What is the primary consideration for designers to achieve high-performance in pipelining?
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What is the consequence of increasing the number of stages in a pipeline?
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What is the cycle time of an instruction pipeline?
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What happens to instructions I4 through I7 in the pipeline at time 8?
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What is the impact of latching delay on instruction cycle time?
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What is the total time required to execute n instructions in a pipeline with k stages, assuming no branches?
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What is the primary function of branch instructions in program execution?
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What happens to the pipeline when a conditional branch instruction is executed?
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What is the performance penalty incurred due to conditional branches?
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What is the role of the execute stage in the pipeline?
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What is the purpose of the instruction decoding stage in the pipeline?
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How are operands calculated in the pipeline?
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What is the benefit of a pipelined architecture?
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What is the significance of the time unit 7 in the pipeline operation?
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Study Notes
Instruction Pipelining
- The CPU fetches instructions from memory in the Fetch Instruction (FI) stage.
- In the Decode Instruction (DI) stage, the instruction is decoded to determine the operation and operands needed.
- If required, effective address calculation occurs in the Calculate Operands (CO) stage.
- The CPU retrieves operands from memory or registers in the Fetch Operands (FO) stage.
- The actual operation is performed in the Execute Instructions (EI) stage.
- Results are stored back into memory or registers in the Write Operands (WO) stage.
Two Stage Instruction Pipeline
- A six-stage pipeline can reduce execution time for 9 instructions from 54 time units to 14 time units.
Conditional Branch
- A branch instruction can be either unconditional (always results in branching) or conditional (may or may not cause branching, depending on some condition).
- Branch instructions are used to implement control flow in program loops and conditionals.
Effect of Conditional Branch on Instruction Pipeline Operation
- When a conditional branch is executed, the pipeline must be cleared of instructions that are not useful.
- This can result in a performance penalty due to the uncertainty of which instruction will come next.
Six Stage Instruction Pipeline
- The pipeline can be depicted as a sequence of events, with time progressing vertically down the figure.
Alternative Pipeline Depiction
- The pipeline can be depicted as a series of stages, with each row showing the state of the pipeline at a given point in time.
Pipeline Performance
- The cycle time of an instruction pipeline is the time needed to advance a set of instructions one stage through the pipeline.
- The cycle time can be determined by considering the number of stages and the number of instructions being processed.
- Factors that affect pipeline performance include:
- Overhead involved in moving data between stages
- Control logic required to handle memory and register dependencies
- Latching delay (time taken for pipeline buffers to operate)
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Description
Quiz on instruction pipelining, covering stages of pipelining including fetch instruction, decode instruction, and more, from William Stallings' Computer Organization and Architecture Design.