1.1.2 CPU Performance

Give three characteristics of a CPU that can affect its performance.

• Clock speed

• Cache size

• No. of cores

What is clock speed?

• Number of cycles clock sends per second — measured in Hz

• 1GHz = 1 billion cycles per second

What effect does higher clock speed have on CPU performance?

• More FDE cycles per second

• More instructions processed in given time

• Improves performance

What effect does cache size have on CPU performance?

• Larger cache = more frequently used data and instructions stored

• Reduces no. of times CPU accesses main memory

What is cache?

Memory that provides fast access to frequently used instructions and data

Explain one reason why the cache size affects the performance of the CPU.

• Data transferred faster

• Makes CPU more efficient

What is a core?

Processing unit inside CPU

What effect does the number of cores have on CPU performance?

Multiple instructions can be processed simultaneously — improves performance

Why won’t doubling cores always double performance?

• Cores must communicate

• Some programs aren’t designed to use multiple cores

• The specification of two CPUs is shown in Fig. 1.

Computer 1	Computer 2
Clock Speed: 1 GHz	Clock Speed: 1.4 GHz
Cache size: 2 MB	Cache size: 2 MB
Number of Cores: 4	Number of Cores: 2

• When running a 3D flight simulator, Computer 1 is likely to run faster than Computer 2.

Using the information in Fig. 1, identify one reason for this. [1]

More cores

• The specification of two CPUs is shown in Fig. 1.

Computer 1	Computer 2
Clock Speed: 1 GHz	Clock Speed: 1.4 GHz
Cache size: 2 MB	Cache size: 2 MB
Number of Cores: 4	Number of Cores: 2

• When running a 3D flight simulator, Computer 1 is likely to run faster than Computer 2.

Identify two other parts of a computer that are not in Fig. 1, which could improve the performance of the computers. [2]

• RAM

• SSD