Internal and external hardware components of a computer

1. Internal and External Hardware Components of a Computer

2. 3 Box model CPU I/O Main Memory Control Bus Address Bus Data Bus System Bus

3. The Processor The most complex and expensive component of the computer. Transistor count is currently 2.6 billion (2011). The processor executes programs and supervises the rest of the system at the same time. Transistors are devices that amplify and switch electronic signals and power. A voltage or current applied to one pair of the transistors terminals changes the currents flowing through another pair of terminals.

4. Main memory is data stores that can be directly addressed by the CPU. It’s used to store program instruction and data and uses the system bus to communicate with the CPU . Main memory is made up of RAM and ROM chips. Today Ram is measured in Gb and large programs can run or multiple programs can run at the same time. The larger the memory the more/bigger the program you can run. Main memory is data stored in different addresses and so the more memory you have the more addresses you have. Main Memory

5. Random access memory or RAM is used for any memory that is readable and writable so the process uses it to store data and load it back. However RAM is volatile, meaning the contents of the RAM is forgotten when the computer is turned off. RAM

6. Read only memory or ROM remembers data when the computer is turned off making it non-volatile. ROM can provide random access like RAM but it can’t be written to. This makes it useful to store fixed programs on. ROM

7. I/O controllers regulate the power between the devices and the processor. Can handle different types of devices now whereas before the processor wouldn’t recognise new devices and whole new CPU would have to be installed. Generic ports are now used for all devices e.g. USB because all computers have them and everyone can plug in devices. This is the method of performing I/O between the CPU and the device. I/O Controllers and Ports

8. In the 3 box model each components is connected by a bus, known as the system bus. The different buses are made up of wires that connect to each component of the computer system and passes signals between them. Signals either represent an address, data or control information and so the system bus is made up of the address bus, the data bus and the control bus. Connection between devices

9. Unidirectional and has 32 wires connecting to the address memory which gives 110 locations. It carries signals from the CPU to the main memory and I/O devices. The CPU could request some data from the main memory and it does this by sending the address of the data to the main memory and then the main memory returns the data along the data bus . Address Bus

10. Bidirectional and has more than 16 wires (usually 32) and is transports control signals between the 3 components of the box model. It’s used to carry important information such as messages to say when a device has finished a job or when a device has been plugged in. It controls interrupt signals as well which allow devices to signal that they have finished a request. The CPU temporarily suspends its current program, services the device and then resumes its program. Ctrl + Alt + Del is the highest priority of interrupt . Control Bus

11. Bidirectional and has 32 wires used to transport data and instruction between all the components in the 3 box model. The larger the data bus is the more data that can be transported at one time. E.g. 11111111 = 8 digit’s which means the data bus is 8 bit. Data Bus

12. Peripherals are any device that isn’t connected to the CPU . I/O devices aren’t connected to the CPU – meaning they are peripheral. The system uses them to get information in or out. E.g. a keyboard gets information in and a VDU gets information out. Peripherals

13. Secondary storage is not directly connected to the processor making it a peripheral device but it is permanent storage. An example of secondary storage is a magnetic hard disk. Any secondary storage is connected to the processor and the main memory by an I/O controller and data is transferred by using the system bus. Secondary Storage