1.2 Processor Performance

Question 1

What does the width of an address bus determine?

Answer 1

The maximum possible memory addresses of the system

Question 2

Bi-directional data bus

Answer 2

Data can be sent both ways along the bus

Question 3

What are the main factors that can affect CPU performance?

Answer 3

• Clock speed
• The number of cores in the processor
• The amount and type of cache memory

Question 4

Why does clock speed affect CPU performance?

Answer 4

The faster the clock speed, the faster a computer can fetch, decode and execute instructions

Question 5

How does the system clock?

Answer 5

A sequence of frequent on and off signals are used to synchronise the operations of the components (actions are carried on the rising edge of the clock, which take a fixed number of cycles to complete)

Question 6

Why does the number of cores affect CPU performance?

Answer 6

Each core in theory can process different instructions simultaneously making its own fetch-decode-execute cycle (although some software may not be able to take full advantage of all four processors

Question 7

Parrallel processing

Answer 7

Using several processor cores working at the same time

Question 8

Why is parallel processing not always possible?

Answer 8

Instructions are processed sequentially

Question 9

Cache

Answer 9

A small amount of superfast (but expensive) memory that stores data and instructions that have been recently been used by the processor

Question 10

What is L1 cache split into?

Answer 10

Instruction cache and data cache so that data and instructions can be fetched simultaneously

Question 11

Pipelining

Answer 11

A technique used to improve performance, by example overlapping stages in the fetch-exectue cycle, or by breaking down the stages in an arithmetic instruction

Question 12

Pipeline example

Answer 12

• An instruction enters the pipeline, and as soon as one stage has been completed, another instruction enters the pipeline
• A third instruction then enters before either of the others is completed

Question 13

What are all the factors that can affect CPU performance?

Answer 13

• Clock speed
• Corse
• Size and type of cache
• Size of address bus which determines maximum size of RAM
• Size of data bus determines the maximum size of an operand in an instruction
• Pipelining is used to improve efficiency