Class Notes

Introduction to computers

What is a computer?
This is an electronic device, which accepts data (input), processes this data (input) to produce information (output) and stores or information (output) over a communication media.

What makes a computer powerful

- Speed - a computer can do billions of actions per second
- Reliability – failures are usually due to human error, one way or the other
- Storage – a computer can keep huge amounts of information


Types of computers

- Supercomputer
- Mainframe
- Minicomputer
- Microcomputer
- Personal Digital Assistant

Supercomputer
This is fastest computer currently available. Their speed is measured in floating point per second. They are superior to other computers in terms of processing speed, memory size, physical size and cost.

Uses
- Scientific simulations
- Weapon research
- Nuclear energy
- Meteorology

Mainframes
Mainframe computers are relatively smaller than supercomputers and are designed primarily to support enterprise-wide information system frequently referred to as enterprise servers. It processes data at a rate of millions instructions per second (mips). Mainframes can process a number of applications concurrently. They are mainly used in large organizations where many users at separate workstations must share the same computer.

Uses
- Federal and local government agencies
- Banks
- Hospitals
- Industrial users

Minicomputers
Minicomputers were developed for doing specialized tasks. They are smaller, less powerful, and less expensive than super and mainframe computers.
Uses
- Used in scientific labs
- Engineering firms
- Industrial manufacturing plants
- Used for the numeric control machines

Microcomputer
The microcomputer is also known as the personal computer (PC). It was designed for general use by a single person.
Uses
- Domestic use
- Small business
- Used to teach students where teachers are not available
Types of computers
- Desktop
- Laptop
- Palmtop
- Notepad

Personal Digital Assistants
This is a specialized hand held computer that is designed to electronically organize all of your personal information.

Uses
- Telephone book
- Address book
- Appointment calendar
- Notepads

Functions of a computer

A computer has four functions:

Accepts data Input
Processes data Processing
Produces information Output
Stores results Storage

The information processing cycle

Input
Processing
Storage
Output




Components of a computer system

Hardware The physical parts of the computer. Hardware includes:
- CPU
- Input devices
- Output devices

Software the programs (instructions) that tell the computer what to do.

User without people/users the computer is useless.

Data text, numeral, graphics and sound that is entered into the computer.


The computer system

CPU
This is the brain of the computer. CPU stands for Central Processing Unit, which controls all of the core functions (processing) of the computer.

Input devices
Input devices are devices through which data is entered and transformed into machine-readable form.

Types of input devices
- Keyboard – used to enter data into the computer
- Mouse – used to point and click on menus, buttons, icon etc.
- Scanner – operates in a similar manner as a photocopier
- Digital camera – this camera stores photographed images electronically
- Gaming devices – used for playing computer games.

Output devices
An output device accepts data that has been processed into useful form (information).

Types of output devices
- Monitor – this is used to display the data that is processed by the CPU (information).
- Printer – this used to put on paper what you see on the monitor.
- Speaker – this is used for making sound audible.

Types of output
1. Hard copy – printed on paper or on transparencies
2. Soft copy – displayed on a monitor or screen.

Peripheral devices
These are input and output devices (hardware) that is attached to the system unit.
e.g. Printer, monitor, keyboard, mouse, etc.



Primary Storage Storage


Storage refers to the media and methods used to keep information available for later use.

Memory storage falls into two categories:
- RAM – Random Access Memory. This is known as volatile memory, that is, information is lost when the power is switch off. RAM stores data that are currently being used by the CPU. RAM stores data for processing and it also stores instructions for processing the data.

- ROM – Read Only Memory. This can be read but not written to and is non-volatile, that is, the data in it are stored permanently. ROM contains startup information for your computer system.

Secondary Storage

Secondary storage is needed because memory storage (RAM, ROM), may be limited in size and are temporary.

Categories of secondary storage
- Direct access storage – this is where any data can be accessed without reading any other data item first.
- Sequential access storage – this is where all data between present position of the read/write head and the required data has to be passed over before the data has to be accessed

Direct access storage devices
- Floppy disks
- Jazz/ Zip disk (memory stick, jump drive etc)
- Hard disk/hard drive
- Optical disk (CD-ROM, CD-R, CD-RW)
- DVD (DVD-ROM, DVD-R, DVD-RW)

Sequential access storage devices
- Magnetic tape

Care of floppy disks
A floppy disk is a sensitive device and should be treated with care. The following are some of the ways in which floppies should be cared for:
- Do not expose the floppy to extreme weather conditions (sunlight, rain, dew).
- Do not remove disk when the light indicating that the computer is using the diskette is on.
- Do not spill liquid on diskette
- Keep floppy disk away from magnet

When a floppy is used for the first time it should be formatted. Formatting is done to prepare the diskette for reading information from it and writing information to it.

Types of software
- System software
- Application software

System software is a set of programs that manages the resources of the computer system
e.g. User interface-(menus) graphical user interface-( icons, pop-up and drop-down menu. Operating system –UNIX, Windows 98, Windows 2000, Windows XP.

Application software is used to solve specific user tasks.
e.g Word processing package – Microsoft Word, Spreadsheet package – Microsoft Excel

Data Security
This is the system of safeguards that protects software and data from theft and modification. E.g. Passwords, people control, encryption.


Data Integrity
This is ensuring that data is correctly inputted from the source and remain correct as long as it is needed.

Microsoft Excel Tutorial

CARRY OUT DATA ENTRY AND RETRIEVAL PROCEDURES

This blog is designed to provide reference material and class work for the unit "CARRY OUT DATA ENTRY AND RETRIEVAL PROCEDURES".
Assignments and class work will also be provided.