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Questions and Answers

What challenges are mentioned in assessing the performance of computers?

The sheer scale and intricacy of software systems. (correct)

The limited range of performance improvement techniques.

The simplicity of modern software systems.

The complexity of hardware design and user requirements.

What might salespeople do regarding computer performance?

Steer consumers towards the most affordable options.

Provide accurate and unbiased comparisons.

Avoid discussing performance altogether.

Highlight performance metrics that favor their products. (correct)

What is highlighted as a critical aspect when selecting a computer?

The availability of warranties and support.

The necessity to accurately measure and compare performance. (correct)

The brand reputation of the computer manufacturer.

The visual design of the computer.

What analogy is used to explain the concept of performance?

Evaluating the performance of passenger airplanes. Signup and view all the answers

Which characteristic is specifically noted about the Concorde in the context of performance?

It has the highest cruising speed. Signup and view all the answers

What does CPI stand for in computer architecture?

Cycles Per Instruction Signup and view all the answers

Which computer has a faster CPU time based on the example provided?

Computer A Signup and view all the answers

If Computer A has a clock cycle time of 250 ps and a CPI of 2.0, what is the CPU time for I instructions?

$500I ps$ Signup and view all the answers

What is the formula to compute the CPU clock cycles for a computer?

CPU clock cycles = Instructions x CPI Signup and view all the answers

Which component is NOT necessary for calculating CPU time based on the example provided?

Memory size Signup and view all the answers

Based on the provided example, what is the clock cycle time for Computer B?

500 ps Signup and view all the answers

What does a higher CPI indicate about a computer's performance?

It requires more clock cycles per instruction Signup and view all the answers

If no instructions are executed (I=0), what would be the CPU time for both computers?

0 ps for both computers Signup and view all the answers

What is Turbo mode in Intel processors?

A feature that temporarily enhances the clock rate by about 10%. Signup and view all the answers

If a Java application originally takes 15 seconds to run, what would be the expected runtime using the new compiler that reduces the instruction count but increases CPI?

9.9 seconds Signup and view all the answers

What is the relationship between clock rate and power in Intel microprocessors over the years?

Both increased rapidly for decades but then flattened or dropped off recently. Signup and view all the answers

Why have recent generations of Intel microprocessors experienced a slowdown in clock rate and power increase?

Because of the practical power limit for cooling microprocessors. Signup and view all the answers

What does the increase in CPI imply when switching to the new Java compiler?

The new compiler increases the number of cycles per instruction executed. Signup and view all the answers

What is typically prioritized to maximize computer performance?

Minimize response time Signup and view all the answers

What effect does replacing a processor with a faster version generally have?

Improves both response time and throughput Signup and view all the answers

When additional processors are added to a system that handles separate tasks, what primarily increases?

Response time remains steady while throughput increases Signup and view all the answers

How do changes in throughput and execution time generally relate to each other?

Higher throughput can lead to increased response time during high demand Signup and view all the answers

What is a common goal when benchmarking personal mobile devices versus servers?

Prioritize response time for mobile devices and throughput for servers Signup and view all the answers

What is one way in which an algorithm's use of divides affects its performance?

It tends to result in a higher CPI. Signup and view all the answers

How does the programming language affect instruction count?

By determining the number of processor instructions needed. Signup and view all the answers

Which aspect of performance is directly influenced by the efficiency of the compiler?

Instruction count and average CPI. Signup and view all the answers

What does the instruction set architecture impact?

All three aspects of CPU performance. Signup and view all the answers

What is the relationship between CPI and IPC?

They are inversely related; higher CPI means lower IPC. Signup and view all the answers

Why might some processors achieve a CPI less than 1.0?

They can fetch and execute multiple instructions per clock cycle. Signup and view all the answers

What does varying clock rates in modern processors allow for?

Temporary boosts in performance and energy savings. Signup and view all the answers

What is typically expected regarding the minimum CPI of a processor?

It can go below 1.0 depending on IPC. Signup and view all the answers

Study Notes

Performance Assessment

Assessing computer performance is complex due to modern software complexity and various hardware improvement techniques.
Accurate performance measurement is crucial for both purchasers and designers, influencing purchasing decisions.
Understanding measurement techniques and their limitations aids in selecting the right computer for specific applications.

Defining Performance

Computer performance can be defined by various metrics, such as speed, range, and capacity, similar to passenger airplanes.
Metrics for measuring performance differ based on application types; mobile devices prioritize response time, whereas servers focus on throughput.

Throughput and Response Time

Replacing a processor with a faster version generally improves both response time and throughput.
Adding additional processors increases throughput but may not enhance response time for individual tasks, depending on demand.

Performance Metrics

Primary focus on minimizing response time or execution time in early discussions of computer performance.
Average cycles per instruction (CPI) serves as a comparative measure across implementations of the same instruction set architecture.

Performance Equation Example

For two computers executing 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.
By calculating CPU clock cycles and CPU time for both computer A and B, Computer A is determined to be faster.

Factors Influencing Performance

Programming languages impact instruction count and CPI due to how they translate high-level statements into processor instructions.
Compilers affect both instruction count and CPI by determining how source language instructions are translated into machine code.
Instruction set architecture influences overall CPU performance, affecting the number of required instructions and their execution cycles.

Performance Characteristics

Some processors can execute multiple instructions per clock cycle, expressed as instructions per clock cycle (IPC), which can invert the traditional CPI calculation.
Modern processors may vary their clock rates to save energy or boost performance temporarily, requiring average clock rate calculations for accurate measurements.

Real-World Scenario

A Java application that runs for 15 seconds on a desktop will potentially run faster under a new compiler that reduces instruction count but increases CPI, showcasing the trade-offs in performance optimization.

The Power Wall

Historical data shows rising clock rate and power for Intel processors over 36 years, leading to a recent plateau due to practical power limits in cooling.

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Description

This quiz delves into the complexities of assessing computer performance. It explores the various factors that influence performance measurement, including software systems and hardware design techniques. Understanding these elements is essential for making informed decisions when comparing different computer systems.

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