CPU performance Practice Questions

Question 1

What is the purpose of the clock in a computer system?

Accepted Answer

To synchronize the operations of the CPU and other components — The clock generates a steady pulse that synchronizes all computer operations. Each pulse triggers a step in the fetch-execute cycle, ensuring components work in harmony. It does not store data, execute instructions, or manage I/O directly.

Question 2

Explain why increasing the clock speed of a CPU may not always result in a proportional increase in performance.

Accepted Answer

Because other bottlenecks such as memory speed, cache size, and the number of cores can limit performance — Performance depends on many factors. If memory is slow, the CPU may wait for data. Cache size affects how much data is quickly accessible. More cores allow parallel processing. Overheating can cause throttling but is not the primary reason for non-proportional gains. Clock speed is directly related to performance, but not the only factor.

Question 3

A CPU has a clock speed of 3.5 GHz. What does this measure?

Accepted Answer

The number of fetch-execute cycles it can perform per second — Clock speed is measured in hertz (cycles per second). A 3.5 GHz CPU can perform 3.5 billion cycles per second. Each cycle typically corresponds to one fetch-execute cycle, though modern CPUs may do more per cycle. It does not directly measure data amount or transfer speed.

Question 4

A computer system has a CPU with a clock speed of 3.0 GHz and a single core. Which of the following best describes the effect of increasing the clock speed to 3.5 GHz on the performance of the system?

Accepted Answer

It will increase the number of instructions executed per second, but may not double the performance due to other bottlenecks. — Increasing clock speed increases the rate at which the CPU executes instructions, so more instructions per second can be processed. However, overall performance also depends on other factors like memory speed, cache size, and the efficiency of the instruction set. Therefore, performance improves but not necessarily proportionally.

Question 5

A computer has a CPU with a clock speed of 3.0 GHz. Approximately how many clock cycles occur in one second?

Accepted Answer

3 billion — 1 GHz equals 1 billion cycles per second. Therefore, 3.0 GHz means 3 billion cycles per second. This is a common conversion error: students often confuse MHz with GHz or misplace the decimal.

Question 6

Which of the following best explains why a CPU with a higher clock speed does not always perform faster than one with a lower clock speed?

Accepted Answer

Other factors like cache size, number of cores, and architecture affect performance; clock speed is only one factor. — While clock speed (GHz) indicates how many cycles per second, the actual instructions per cycle (IPC) and other architectural features (pipelining, cache, cores) determine overall performance. A CPU with lower clock speed but higher IPC can outperform one with higher clock speed but lower IPC. Also, thermal throttling can reduce performance, but that is not the primary reason.

CPU performance

Subtopics in this area

CPU performance Revision Guide

Learning Objectives

Sample Exam Questions

Related Topics in OCR GCSE Computer Science

Additional programming techniques

Boolean logic

Programming fundamentals

Primary storage (memory)