1. Computer Structure & Architecture 7b - CPU & Buses

2. Lesson 3 – Structure of the CPU LI:Identify and describe the purpose of the main components of the CPU

3. Structure of the Processor The CPU is made up of the processor and main memory. The processor is like the brain of the computer as it controls all of the other components and manages the execution of programs and instructions. The processor has 3 main components: ROM RAM InputOutput Backing Storage Control Unit Registers ALU

4. Structure of the Processor Control unit: This controls the fetching, decoding and execution of program instructions held in main memory. ALU (Arithmetic Logic Unit): The ALU performs arithmetic (+, -, x, /) and logical decisions such as AND or OR. Registers: These are temporary storage location within the processor that have very fast access and are used to hold single items of data, such as the next instruction to be decoded or the next location in main memory to be accessed. Control Unit Registers ALU

5. Main Memory Main memory is located with the CPU and is made up of 2 components: ROM (Read Only Memory): Cannot write data to ROM (only read) Keeps it contents when the computer is switched off Stores the instructions to load the main operating system RAM (Random Access Memory): Instructions and data can be written to RAM It loses its contents when the computer is switched off Stores the programs and data that the user is currently using ROM RAM

6. Lesson 4 – Buses LI:Identify and describe the purpose of the 3 main buses in a computer system.

7. Buses There are 3 main buses in a computer system: Address Bus Used to specify the address of the memory location to read from/ write to It is a uni-directional bus (processor  memory) Data Bus Used to transfer data between the processor and main memory It’s a bi-directional bus (processor  memory) Control Bus The control bus does not carry any data It’s a collection of lines (or ‘switches’ ), each with a specific function e.g. Read line, write line, clock.

8. Buses Control Bus Data Bus Address Bus Control Unit Registers ALU Memory