1. COMPUTER SYSTEM
A computer system is define as combination of components designed to process data and store files.
A computer system consists of four major hardware component; input devices, output devices, processor and storage devices.
To make sure the computer system fully function, it needs:
Hardware
Computer hardware consists of;
Input devices
Processor
Output devices
Storage

2. Software
System Software  BIOS program, Operating System, utility programs and programming languages.
Application Software  word processing, spreadsheets, databases, accounting, games, internet browser etc.
User
Computer user refers to the person who uses a computer for any purposes such as for work, business or entertainment.

3. INFORMATION PROCESSING CYCLE
User will input data to be process by the processor.
The storage hold database, files and programs. The output devices present the processed data as useful information products for the user.

4. Input devices
When data is entered in the computer system, it is called an input. Input comes in various forms; texts, graphics, audio and video.
Example : keyboard, mouse, scanner, digital camera and barcode reader.
Process
For every instruction, the control unit repeats a set of four basic operations called the machine cycle:
Fetching – process of obtaining a program instructions or data item from memory.
Decoding – process of translating a program instruction into signal that a computer can execute.
Executing – process of implementing the instructions in a program.
Storing – process of writing the result to the storage or memory.

5. Output devices Storage devices
Output is a result of raw input data that has been processed by the cpu into meaningful information. Common forms of output; texts, numbers, graphics, sounds, animations and videos.
Example : computer screen, speaker and printer.
Storage devices
System primary storage is RAM, but it can only hold data temporarily. Thus, secondary storage is needed to provide additional storage and the data stored in it is consider permanent until it is deleted.
Example : hard disks, rewritable CDs and DVDs, diskettes and pen drive.
Central Processing Unit (CPU)
CPU is the brain of computer. All processing activities are done in the CPU.
The processor must be connected to input devices, output devices and storage devices to carry out task.

6. DATA REPRESENTATION Binary digit
Computer recognise only two discrete states: on and off.
These states can be represented y two digits, 0 and 1.
Each 0 or 1 is called bit in a binary system.
Bit
A bit is the smallest unit of data that the computer can process.
Besides than represent the states on and off, a bit also represent true and false or yes and no.
Byte
Is a unit of information built from bit. One byte is equal to 8 bits.
One byte represents a single character such as the number 3, letter b or a symbol.
Character
One byte represent one character such as a, and many more.
There are three character codes to represent character which are ASC!!, ABCDIC and Unicode.

7. INTRODUCTION TO BINARY CODING
Before the use of ASCII, character codes were widely use as a medium for communication. Some of the character codes used are:
Morse code ( )
Telegraph ( )
Hollerith Code ( )
ASCII 1963
What is ASCII??
ASCII is a standard of 7-bit code used to represent characters, which include letters, numbers and punctuation marks.
7-bit allow the computer to encode 128 characters for the numbers 0-9, uppercase and lowercase letters A-Z and also punctuations.

8. Functions of ASCII
To achieve compatibility between various types of data processing equipment making it possible for the component to communicate with each other successfully.
Enable manufacturers to produce components that are assured to operate correctly in a computer.
Make it possible for human to interact with a computer.
Enables users to purchase components that are compatible with their computer configurations.

9. DATA MEASUREMENTS Kilobyte (KB) In mathematics, 1KB = 1000 bytes
In computer, 1KB = 1024 bytes or 2 bytes.
Megabyte (MB)
1MB = bytes or 1MB = 2 bytes.
Gigabyte (GB)
1GB = or 1GB = 2 bytes
Terabyte (TB)
1TB = or 1TB = 2 bytes

10. CLOCK SPEED MEASUREMENT
A clock speed unit is measured in Hertz.
Megahertz (MHz)
Mega is a prefix that stands for million.

11. Gigahertz (GHz)
Giga is a prefix that stands for billion.
Processing speed
The system clock is one of the major factors that influence the computer speed.
A CPU with the higher clock speed can process more instructions per second. For example, a 1GHz CPU is faster than a CPU operating at 800 MHz.
Microprocessor speed
Microprocessor speeds are determined by their clock speed and are usually expressed in GHz, billion of machine cycle per second.
SPEED AND PATH
A combination of speed and number of paths determines the total processing speed or channel bandwidth.