1. Computer Systems Nat 4/5 Computing Science Computer Structure:
Lesson 1:
Processor Structure

2. Lesson Aims By the end of this lesson: Pupils at will be able to:
Label a computer system in terms of a 5 block diagram
Describe the phrase ‘word length’
Describe the purpose of a processor
List and describe the parts of a processor:
Control Unit, ALU, registers
Describe what a bus is and does

3. A Basic Computer System
Nat 4/5
A Basic Computer System
Backing Storage
Output
Devices
Input Devices
Processor
Memory
This is known as the 5 block diagram.

4. The 5 Block Diagram Input Devices Output Devices Memory
Nat 4/5
The 5 Block Diagram
Input Devices
These are devices that enter data INTO the computer. i.e. Keyboard and mouse
Output Devices
These are devices that generate output FROM the computer i.e. printer.
Memory
There are two types of memory. RAM and ROM (more on this later)
Backing Storage
This is required to store permanent copies of our files.

5. Arithmetic and Logic Unit (ALU)
Nat 4/5
The Processor
The processor is the ‘brain’ of the computer.
It is the piece of equipment that actually performs the instructions required.
It can be shown in the following diagram:
Processor
Control Unit
Arithmetic and Logic Unit (ALU)
Registers

6. Processor Parts Control Unit Arithmetic and Logic Unit (ALU) Registers
Nat 4/5
Processor Parts
Control Unit
This controls the order of execution and the timing of instructions
Arithmetic and Logic Unit (ALU)
This performs the calculations for the processor. It also carries out the Logical decisions.
Registers
These are temporary stores of information, at best they will store a few bytes of information.

7. Nat 4/5
32 bit and 64 bit computing?
You often hear a processor being described as 32 bit or 64 bit.
This is usually referring to the ‘word length’ of the computer
This is the largest binary number that the processor can manipulate in one operation.

8. What does a bus do? Control Unit RAM Registers
Nat 4/5
What does a bus do?
Processor
Main Memory
Control Unit
Data Bus
RAM
ALU
Address Bus
ROM
Registers
A bus is a collection of wires which can carry data

9. Buses Data Bus Address Bus
Nat 4/5
Buses
Data Bus
The data bus is used to carry data to and from the CPU and Memory.
It will hold a binary word.
Address Bus
This carries the address of the memory location that is being used

10. Mnemonic – CAR(s) Summary
Nat 4/5
Summary
The CPU (Central Processing Unit) is the heart of the computer
The CPU has 3 main parts
Control Unit
Controls the timing and order of execution
Arithmetic and Logic Unit (ALU)
Performs the arithmetical and logical functions
Registers
Temporary stores of information
Word length is the length of the biggest binary number that the processor can process in one operation
Mnemonic – CAR(s)