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# CPI Execution: Average Memory Access Time (AMAT)

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@AmbitiousBoron

### What is the formula for Memory Stall Cycles per Average Instruction (CPIStall), and how does it relate to MemAccess/Instruction and MemStall?

CPIStall = (MemAccess/Instruction)(MemStall) = (1 + %load + %store)(1 – hi)(Mi)

### What is the Ideal CPI, and how does it relate to CPIPerfect and CPIStall?

CPI = CPIPerfect + CPIStall, and in the ideal case, CPIStall = 0, so CPI = CPIPerfect

### What is the calculation for AMAT, and how does it relate to MemStall?

AMAT = 1 + MemStall, where MemStall = (Miss Rate)(Miss Penalty)

### What is the Speedup of Ideal CPI, and how does it relate to CPI and CPIPerfect?

<p>Speedup = CPI/CPIPerfect, where CPI = CPIPerfect in the ideal case</p> Signup and view all the answers

### In a system with no cache, what is the miss rate, and how does it affect MemStall?

<p>The miss rate is 1, resulting in MemStall = (1)(Miss Penalty)</p> Signup and view all the answers

### In the example given, what is the calculation for CPI, and how does it relate to CPIPerfect and CPIStall?

<p>CPI = CPIPerfect + CPIStall = 1.1 + 140 = 141.1</p> Signup and view all the answers

### What does the Average Memory Access Time (AMAT) represent in the context of CPU execution?

<p>The number of cycles required to complete an average memory access request by the CPU.</p> Signup and view all the answers

### Derive the formula for AMAT in terms of hit rate, access time, miss rate, and miss penalty, given that the hit access time t1 is usually 1 cycle and the miss penalty is T2.

<p>AMAT = ti + (mi)(T2) or AMAT = 1 + (mi)(T2) since ti = 1.</p> Signup and view all the answers

### What is the significance of the term MemStall in the context of CPU execution, and how is it related to AMAT?

<p>MemStall represents the memory stall cycles per memory access, and it is equal to (m1)(T2) or (Miss Rate)(Miss Penalty). AMAT is directly affected by MemStall, with the formula AMAT = 1 + MemStall.</p> Signup and view all the answers

### What is the relationship between the hit rate (hi) and miss rate (mi) in the context of CPU memory access?

<p>The miss rate (mi) is equal to 1 – hi, indicating that the sum of the hit rate and miss rate is always equal to 1.</p> Signup and view all the answers

### What is the implication of a higher miss rate on the Average Memory Access Time (AMAT)?

<p>A higher miss rate leads to a higher AMAT, as it increases the number of stall cycles added to the CPU execution cycles for one memory access.</p> Signup and view all the answers

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