CPU Performance and Measurement Techniques

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Questions and Answers

What is a key characteristic of RISC architecture?

Has over 500 instructions in its instruction set

Focuses on high performance with low-power consumption (correct)

Uses complex instructions requiring multiple cycles

Allows program changes to be incompatible with older versions

Which of the following statements about CISC architecture is true?

It has a smaller instruction set compared to RISC

All instructions can be executed within 1 clock cycle

The MULT instruction can execute an entire multiplication task in one line of code

It supports backward compatibility with older program versions (correct)

What is the main focus of ARM architecture?

Large size and cost-effectiveness for servers

High power consumption for desktop computing

Dedicated functions for embedded systems (correct)

Execution of complex instructions over multiple cycles

Which of the following best describes the execution process in CISC for the MULT operation?

Divided into multiple instruction commands Signup and view all the answers

Which feature distinguishes RISC from CISC architectures?

RISC focuses on simplicity and uses fixed instruction sizes Signup and view all the answers

What impact do architectural attributes have on programmers' experience?

They determine the number of bits used to represent data types Signup and view all the answers

How do CISC and RISC differ in terms of instruction execution?

CISC typically emphasizes complex instructions Signup and view all the answers

What is one of the main advantages of using CISC architecture?

The ability to execute extensive tasks with fewer instructions Signup and view all the answers

What are the three key factors that determine CPU performance?

Instruction count, CPI, Clock cycle time Signup and view all the answers

What does MIPS stand for in the context of CPU performance?

Million Instructions Per Second Signup and view all the answers

How is the execution time calculated in the CPU performance equation?

Execution time = Instruction count × CPI × Clock cycle time Signup and view all the answers

Which statement correctly describes the relationship between clock rate and clock cycle time?

Clock rate is the inverse of clock cycle time Signup and view all the answers

Given a clock rate of 400 MHz, how is it expressed in terms of seconds for clock cycle time?

2.5 ns Signup and view all the answers

What is the average CPI if the instruction mix consists of 60% CPI of 1, 18% CPI of 2, 12% CPI of 4, and 10% CPI of 8?

2.24 Signup and view all the answers

In the MIPS rate equation, which part represents the execution time?

Execution time Signup and view all the answers

What will be the MIPS rate if the instruction count is 2 million, the average CPI is 2.24, and the clock rate is 400 MHz?

179 MIPS Signup and view all the answers

What is the primary function of a two-level memory system?

To optimize speed and cost by organizing memory Signup and view all the answers

What happens to the access time as memory capacity increases?

Access time increases Signup and view all the answers

In the context of memory hierarchy, which type of memory is considered volatile?

Primary semiconductor memory Signup and view all the answers

What does the hit ratio (H) represent in a two-level memory system?

The probability of data being found in the faster level Signup and view all the answers

Which of the following correctly describes the relationship between access time and cost per bit?

As access time decreases, cost per bit increases Signup and view all the answers

What is indicated by a high hit ratio in a two-level memory system?

The CPU frequently accesses Level M1 successfully Signup and view all the answers

In the formula for total access time per word, what does (1 - H) represent?

The probability of needing to access Level M2 Signup and view all the answers

How is the average time to access a word calculated in a two-level memory system?

Based on the hit ratio and the access times of both memory levels Signup and view all the answers

What is the relationship between clock rate and clock cycle time?

Clock rate is the inverse of clock cycle time. Signup and view all the answers

To improve CPU performance, which of the following approaches is NOT recommended?

Increase the clock cycle time. Signup and view all the answers

If a program runs in 10 seconds on a computer with a 2 GHz clock rate, what is the total number of CPU clock cycles needed for that program?

20 × 10^9 clock cycles Signup and view all the answers

When designing computer B, which factor is said to increase by 1.2 times compared to computer A?

Number of CPU clock cycles needed Signup and view all the answers

If computer B runs the same program in 6 seconds, what can be inferred about the performance change compared to computer A?

Computer B has improved performance despite needing more clock cycles. Signup and view all the answers

What is the formula for calculating execution time for a program?

Execution time = Number of clock cycles / Clock rate Signup and view all the answers

What factor influences how much data can be processed in a fixed time at the same conditions?

Clock cycle time Signup and view all the answers

What is the effect of a higher clock rate on CPU data processing?

More data can be processed in a shorter time. Signup and view all the answers

What does CPI stand for in the context of CPU performance?

Cycles Per Instruction Signup and view all the answers

If Computer A has a CPI of 2.0 and Computer B has a CPI of 1.2, which statement is true regarding their performance?

Computer B is expected to perform better due to a lower CPI. Signup and view all the answers

How is the total number of CPU clock cycles calculated?

Total Instructions multiplied by CPI Signup and view all the answers

If the execution time of Computer A is less than that of Computer B by 83.33%, what does this indicate?

Computer A is significantly faster. Signup and view all the answers

What is the effect of a lower clock cycle time on CPU performance?

It generally increases overall performance. Signup and view all the answers

What can be inferred if two computers have the same instruction set architecture but different clock cycle times and CPIs?

Performance will vary based on clock cycle time and CPI. Signup and view all the answers

Which of the following factors does NOT directly affect execution time?

Total memory size Signup and view all the answers

Study Notes

CPU Performance

CPU performance is affected by instruction count, CPI (Clock cycles per instruction), and clock cycle time
Execution time is calculated by multiplying instruction count, CPI, and clock cycle time
Clock rate is the inverse of clock cycle time
MIPS (Millions of instructions per second) is a measure of CPU performance
MIPS can be calculated by dividing instruction count by execution time multiplied by 10^6, or by dividing clock rate by CPI multiplied by 10^6

Units of Measurement

Reliable performance measure is time
Execution time is measured in seconds
Instruction count is measured in number of instructions
Clock cycles are counted per program

Example 1.3: CPU Performance

A program requires 2 million instructions on a 400 MHz CPU
Average CPI across instruction types is 2.24
MIPS rate for this program is approximately 179

CISC and RISC Architectures

CISC (Complex Instruction Set Computing) uses complex instructions that may require multiple clock cycles
RISC (Reduced Instruction Set Computing) uses simple instructions that can be executed within one clock cycle
CISC instructions might be divided into multiple RISC instructions

Intel x86 Architecture

CISC processor architecture
Instructions are backward compatible across newer processor versions
Has over 500 instructions

ARM Architecture

RISC-based processor architecture
Used in embedded systems for high performance, low power consumption, small size, and low cost
Billions of embedded systems and millions of computers are produced each year

Computer Architecture & Organisation

Computer architecture defines aspects visible to programmers such as instruction set (RISC or CISC), data types, I/O mechanisms, memory addressing modes
Computer organisation defines the hidden hardware details like signals, control units, and interfaces between memory and CPU

Clock Cycle Time or Clock Rate

Clock speed of a CPU is measured in clock cycle time or period (T)
Clock rate or clock speed is measured in frequency (f=1/T)
A 1 MHz processor receives 1 million clock pulses per second
Higher clock rate means that more data can be processed within a fixed amount of time under the same conditions

Processor Performance

Performance factors are the number of clock cycles and clock cycle time
Execution time for a program is calculated by multiplying the number of clock cycles needed by the clock cycle period
To improve CPU performance, you can either reduce the number of clock cycles needed for a program or reduce clock cycle time (increase clock rate)

Example 1.1: CPU Performance

Computer A with a 2 GHz clock rate takes 10 seconds to run a program
Computer B, designed to execute the same program in 6 seconds, requires 1.2 times the clock cycles of Computer A
To achieve this , Computer B needs a 4 GHz clock rate

Instruction Performance

Execution time also depends on instruction count and clock cycles per instruction
CPI (Clock cycles per instruction) is the average number of clock cycles per instruction for a program
CPI can vary between different instructions
Total clock cycles needed for a program are calculated by multiplying instruction count with CPI

Example 1.2: Instruction Performance

Two computers with the same architecture execute the same program
Computer A has a clock cycle time of 250 ps and a CPI of 2.0
Computer B has a clock cycle time of 500 ps and a CPI of 1.2
Computer A is faster because it takes less time to execute the program

Memory Hierarchy

Design constraints involve memory size, speed, and cost
Smaller, faster, and more expensive memories are prioritized, while larger, slower, and cheaper are supplementary
Primary memories are volatile and semiconductor-based
Secondary memories are non-volatile and external
Memory hierarchy exists to balance these factors

Performance of Accesses & Levels of Memory

M1 is a smaller, faster, and more expensive memory level, while M2 is larger, slower, and cheaper
CPU accesses data directly if it's in M1, but data in M2 needs to be transferred first
M1 contains recently accessed instructions and data for faster access
Hit ratio (H) indicates the probability of finding data in M1
Average access time is calculated considering hit ratio, access times for M1 and M2

Example 2.3: Accesses with 2 Levels of Memory

M1 has 1000 bytes with a 0.01 μs access time
M2 has 100,000 bytes with a 0.1 μs access time
Hit ratio is 95%
Average access time is 0.015 μs

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Description

This quiz covers the key concepts of CPU performance, including instruction count, CPI, clock cycle time, and MIPS. Additionally, it explores units of measurement used in assessing execution time and performance. Test your understanding of these fundamentals in CPU architecture and performance metrics.