* A computer system can be represented in either a logical or physical form.

* Both useful are in understanding computer system theory.


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* The actual hardware as seen in the real life

* Contains micro-electrons & physical mechanisms

* Power by electricity

* Very detailed & complex

* Difficult to fully understand without a working knowledge of electronics


* A basic model of computer system

* The model is built from a number of different blocks

* Each block performs a different task

* All blocks work together to process data into information

* Model is conceptual

Input Output

Mouse Printer

Keyboard Monitor

Microphone Speakers



Input Device

� An input device is a device which lets the user feeds data into the computer

� It converts data into a stream of electronic digital signals

� The digital signals get converted into binary inside the computer

� Examples of real-world input devices; keyboard, mouse, light pen, scanner, microphone, camera, motion sensors, biometric devices such as a fingerprint scanner, OMR/OCR readers for direct data capture etc.

Main Memory

� The main memory stores the data before being processed by CPU

� It stores the program being executed by computer

� It is temporary when power is removed, data is lost

� It is often known as RAM (Random Access Memory)

� Stores processed data before it is output

� Contents are filled by input devices, backing storage or the CPU

� Data that needs to be saved is written to the backing storage.

Backing Storage

� The backing storage is usually non- temporary, although its contents may be deleted

� It has loads previously stored data into the main memory

� It has loads previously written programs into memory for processing by CPU

� In the real world may be internal or external

� It is usually mechanical (e.g. Hard Drive, CD or DVD Writer) which slows a computer system

� Data is usually read/loaded or written/saved


� CPU stands for Central Processing Unit

� The CPU is also known as the Processor

� The CPU is like computer’s brain

� The speed of the CPU depends on the efficiency/ power of the computer system

� The CPU consists of two sub-systems: The ALU (Arithmetic Logic Unit) and the Control Unit. It performs basic calculations and logical comparisons. The latter co-ordinates and runs the computer’s operations.

Out Put Device

� The out put device converts the processed data, stored in main memory, into a form that can be understood by us as information

� E.g. real-world output devices; monitor (CRT or TFT/LCD), speakers, printer, plotter, robot, etc.

Four essential main pieces of hardware



* Motherboard

* Hard Drive

The essential software is the operating system.

Before can occur on a computer is input needs to take place from keyboard or mouse.

To open word a message is sent to the operating system because that controls the hardware.

When a program loads it has to come from somewhere this is a program called interrupts. When the CPU receives the interrupt it stops what it’s doing and starts another process.

The os asks the CPU system, CPU asks what wants to do, sends message get program word. Os needs to get from the hard drive. Then the os asks the CPU asks ram is there any space in the ram to run this program. Os yes or no, this point is where the CPU ; HD ; RAM are ready. Word is displayed on the screen.


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