Typesof Computers



Computers we use today are classified into four ways i.e.
. Classification by Process
. Classification by Purpose
. Classification by Size and;
. Classification by Processor power.

Classification by Process
Computers in this classification are classified according to how data processed is represented. It is further subdivided into three sub-classifications and these are:-
. Digital computers
. Analog computers
. Hybrid computers.
Digital Computers.
These are computers that process data that is represented in discrete values i.e. discrete values are numbers that can be defined as 1,2,3,4,5,6…etc. an example of a digital computer is a watch.
Analog Computers.
These are computers that process data in a continuous form or measurable quantity/units.

In other words, these are computers that can be used in measurements e.g. weighing speed, temperature, pressure, humidity, etc. an example of an Analog computer is a thermometer, Anemometer.

Hybrid computers
These are computers which have combined features of both the digital and analog computers.
Classification by Purpose:
Computers are classified according to the work they do. These are classified into two i.e. Special Purpose computers and General Purpose computers.
Special Purpose Computers
These are computers designed particularly to handle a particular task or job. Their form of work or operation is restricted in nature e.g. digital watches and calculator.
Lifts in tall buildings also employ the special purpose computers.
General Purposes Computers
These are computers designed to do or solve a wide range of problems or tasks. A typical computer of this kind can perform calculations, keep date and time, word process documents and also store information.
Classification by Size:
General purpose computers are further sub-divided depending on the user capacity and size of the machine. These are classified into three categories i.e.
  • Super Computers
  • Main frame computers
  • Miniframe computers
  • Microcomputers.
Super Computers and Main frame
During the the 1900’s, computers were divided into a category of Maxicomputers which were also called mainframes.
A such computers consumed a whole room and typically cost between $300,000 and $20,000,000.
The fastest maxicomputers were called supercomputers.
There are also Super computers, a term used to describe their abilities to perform certain functions such as extensive processing, speed and their diligence. They are the fastest and highest capacity computers. They are used for world wide weather forecasting and analysis of weather phenomena, oil exploration, etc.

Mainframe Computers:
These are large general purpose computers with extensive processing, storage, input and output capabilities, hence can accommodate many users at a time.
They can support between 500 – 1000 users at a time, each user working separately with a keyboard, and monitor but all using the same processor i.e. central processing unit. (CPU). These were mainly identified during the first generation computers. Mainframe computers are mostly used in companies for data processing and in science laboratories for complex mathematical calculations.

Mainframe computers: Big and powerful
Mainframe computers are the big, powerful, expensive computers used in the background by most large organisations. The power of the mainframe can be distributed amongst many people accessing the mainframe via their own PC.
Organisations such as large insurance companies would use the mainframe to keep track of their policyholders and send out renewal notices.
Micro Computers:
A microcomputer fit on a desk or lap or hand or was embedded in a tiny device.
These are very small computers compared to the mainframe and miniframe computers. They are single users i.e. the Keyboard, Central Processing Unit and Monitor can only be used by one person at a time. 

These computers are also referred to as Personal computers (P.C) or Personal systems (P.S). They are the most widely used computers in our everyday lives. They include:
  • Desktop computers
  • Laptop computers
  • Palm top computers.
Desktop Computers
Many people use desktop computers, or desktops as they are often referred to, at work, home, school, or the library. They can be small, medium, or large in style, and usually sit on a desk. The term desktop actually refers to the casing, or the tower.
The term desktop computer originated when the computer case was wide and flat, and was designed specifically to fit on your desktop with the monitor on top.
Once you add a monitor, mouse, and a keyboard, you have what is typically known as a desktop computer.
Example Desktop Computer
Most desktop computers are easy to upgrade and expand, or add new parts. In addition to expandability, another benefit of desktop computers is the cost.
If the visible computer is used by just one person at a time, it’s called a personal computer (PC).
If the visible computer is used by many people simultaneously, it’s called a powerful server: the powerful server manages many other computers and let them share info with each other. The typical powerful server is big. It sits in a corner of the room, or fills a whole room, or fills several rooms. Powerful servers are used by big organizations (such as the IRS, Social Security, banks, credit-card companies, and insurance companies) to manage your records and the people who want to use them.
A standard desktop computer is a personal computer that’s too big to carry in one hand. It sits on a desk. It has 4 main parts:
A keyboard that lets you type commands to the computer.
A screen (display) that shows you the computer’s answers.
A mouse that you roll across your desk, to indicate which part of the screen interests you.
The system unit, which is a box holding the computer’s brain & memory.
In a standard desktop computer, each of those 4 parts is a separate device. Wires run out of the system unit to the keyboard, screen, and mouse, so the system unit can communicate with them. Here are 2 comments about the system unit:
If the system unit is taller than it is wide, it’s called a tower. The typical system unit is a tower that’s 15" tall and 15" front-to-back but just 7" wide.
 
Here’s how other computers differ.…
In a wireless desktop computer, the keyboard and mouse communicate with the system unit by radio waves instead of wires.
In an all-in-one computer, there’s no separate system unit; instead, the computer’s brain & memory hide behind the screen, in the same case that includes the screen.
The term “desktop computer” is vague: it means “standard desktop computer or wireless computer or all-in-one computer”.
In a desktop computer system, how big is the screen? If the system is modern, its screen size (measured diagonally, from corner to opposite corner) is between 18½" and 27"; the most common size is 20". If the system is older, its screen is smaller (between 12" and 18½").

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