Module 3.4
Task 5- The CPU


A.M.D.G.

The Central Processing Unit is single most important component of any computer system. Everything that happens inside the computer happens because the CPU executes instructions to do useful work.

There are three main parts of a CPU:

  • Control Unit
    The control unit makes the computer carry out each instruction of a program in the right order and controls the other parts of the CPU.
  • Arithmetic and Logic Unit
    The ALU does all of the arithmetic calculations ( + - x ÷ ) and logical decisions (AND OR NOT XOR)
  • Registers
    Registers are temporary storage locations inside the CPU. They hold the instruction and data being used at any one time.

Some processors are more 'powerful' than others but it is difficult to compare different computer systems. There are four main ways to compare different systems:

  • Clock speed - measured in megahertz or gigahertz this controls the rate that instructions can be fetched, decoded and executed by the processor. The faster the clock speed the more instructions can be processed per second therefore the more powerful the processor.
  • Word Size - the word size of a processor is the number of bits that can be fetched from memory in a single operation. The larger the word size, the more data can be processed in a given time therefore the more powerful the processor.
  • MIPS - millions of instructions per second. Different processors have different instruction sets. Some instructions are more complex than others so it is difficult to use MIPS to compare two completely different processors.
  • FLOPS - floating point operations per second. MIPS is not a very good indication of processor performance because different processors have different complexities of instruction. Almost all processors carry out floating point operations (complex maths) in the same way. We can compare processor performance by seeing which processor can carry out the most FLOPS.
  • Search on the Internet for information to complete the table below, include information on two other processors that you can find information on.
Processor Manufacturer Clock Speed Word Size MIPS FLOPS
Pentium III Intel        
Pentium IV Intel        
Celeron Intel        
G4 Apple / Motorola        
XP+ AMD        
           
           

Answer the following questions in your jotter.

1. Why does increasing a computer's word size increase system performance?

2. Use the internet to find the meaning of the terms RISC and CISC. How cane these affect system performance?

3. Why is clock speed not the best method of comparing two processors?

4. Why are Intel Celeron processors cheaper than Intel Pentium processors?

5. How many registers are in modern Pentium processors?

6. What is the meaning of cache memory in relation to processor performance?