CLASSIFICATION OF COMPUTERS

Introduction

The computer has passed through many stages of evolution from the days of the mainframe computers to the era of microcomputers. Computers have been classified based on different criteria. In this unit, we shall classify computers based on three popular methods.

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Categories of Computers

Although there are no industry standards, computers are generally classified in the following ways:

 Classification Based On Signal Type

There are basically three types of electronic computers. These are the Digital, Analog and Hybrid computers.

Digital Computer

Represent its variable in the form of digits. It counts the data it deals with, whether representing numbers, letters or other symbols, are converted into binary form on input to the computer. The data undergoes a processing after which the binary digits are converted back to alpha numeric form for output for human use. Because of the fact that business applications like inventory control, invoicing and payroll deal with discrete values (separate, disunited, discontinuous); they are beset processed with digital computers. As a result of this, digital computers are mostly used in commercial and business places today.

Analog Computer

It measures rather than counts. This type of computer sets up a model of a system. Common type represents it variables in terms of electrical voltage and sets up circuit analog to the equation connecting the variables. The answer can be either by using a voltmeter to read the value of the variable required, or by feeding the voltage into a plotting device. They hold data in the form of physical variables rather than numerical quantities. In theory, analog computers give an exact answer because the answer has not  been approximated to the nearest digit. Whereas, when we try to obtain the answers using a digital voltmeter, we often find that the accuracy is less than that which could have been obtained from an analog computer.

It is almost never used in business systems. It is used by the scientist and engineer to solve systems of partial differential equations. It is also used in controlling and monitoring of systems in such areas as hydrodynamics and rocketry; in production. There are two useful properties of this computer once it is programmed:

1.  It is simple to change the value of a constant or coefficient and study the effect of such changes. 
2.  It is possible to link certain variables to a time pulse to study changes with time as a variable, and chart the result on an X-Y plotter. 

Hybrid Computer

In some cases, the user may wish to obtain the output from an analog computer as processed by a digital computer or vice versa. To achieve this, he set up a hybrid machine where the two are connected and the analog computer may be regarded as a peripheral of the digital computer. In such a situation, a hybrid system attempts to gain the advantage of both the digital and the analog elements in the same machine. This kind of machine is usually a special-purpose device which is built for a specific task. It needs a conversion element which accepts analog inputs, and output digital value. Such converters are called digitizers. There is need for a converter from analog to digital also. It has the advantage of giving real-time response on a continuous basis. Complex calculations can be dealt with by the digital elements, thereby requiring a large memory, and giving accurate results after programming. They are mainly used in aerospace and process control applications.

 Classification By Purpose

Depending on their flexibility in operation, computers are classified as either special purpose or general purpose.

Special Purpose Computers

A special purpose computer is one that is designed to solve a restricted class of problems. Such computers may even be designed and built to handle only one job. In such machines, the steps or operations that the computer follows may be built into the hardware. Most of the computers used for military purposes fall into this class. Other example of special purpose computers include:

1. Computers designed specifically to solve navigational problems. 
2. Computers designed for tracking airplane or missiles. 
3. Computers used for process control applications in industries such as oil refinery, 
4. chemical manufacture, steel processing and power generation. 
5. Computers used as robots in factories like vehicles assembly plants and glass industries. 
6. General Attributes of Special Purpose Computers 
7. Special purpose computer are usually very efficient for the tasks for which they are specially designed. 

They are very much less complex than the General-Purpose Computers. The simplicity of the circuiting stems from the fact that provision is made only for limited facilities. They are very much cheaper than the General-Purpose type since they involve less components and are less complex.

General-Purpose Computers

General-Purpose computers are computers designed to handle wide range of problems. Theoretically, a general-purpose computer can be adequate by means of some easily
alterable instructions to handle any problems that can be solved by computation. In practice however, there are limitations imposed by memory size, speed and the type of input/output devices. Examples of areas where the general purpose are employed include the following:

1. • Payroll 
2. • Banking 
3. • Billing 
4. • Sales analysis 
5. • Cost accounting 
6.  Manufacturing scheduling 
7.  Inventory control 

General Attributes of General-Purpose Computers
General-Purpose computers are more flexible than special purpose computers.
They can handle a wide spectrum of problems.
They are less efficient than the special-purpose computers due to such problems as;
Inadequate storage;
Low operating speed;
Coordination of the various tasks and subsection may take time.
General Purpose Computers are more complex than the special purpose ones.

 Classification of Computers According to Capacity

In the past, the capacity of computers was measured in terms of physical size. Today, however, the physical size is not a good measure of capacity because the modern technology has made it possible to achieve compactness.

A better measure of capacity today is the volume of work that computer can handle. The volume of work that a given computer handles is closely tied to the cost and to the memory size of computer. Therefore, most authorities today accept the price of rental price as the standard for ranking computers.

Here, both memory size and cost shall be used to rank (classify) computer into three main categories as follows:

1. Microcomputers 
2. Medium/Mini/Small Computers 
3. Large Computer/Main Frames. 

Micro Computers

Microcomputers, also known as single board computers, are the cheapest class of computers. In the microcomputer, we do not have a Central Processing Unit (CPU) as we have in the larger computers rather we have a microprocessor chip as the main data processing unit. They are the cheapest smallest and can operate under normal office condition. Examples are IBM, APPLE, COMPAQ, Hewlett Packard (HP), Dell Toshiba, e.t.c.

Different Types of Personal Computers (Micro Computers)

Normally, personal computers are placed on table desk hence they are referred to as desktop personal computers. Still other types are available under the categories of personal computers. They are:

Laptop Computers are small size types that are battery-operated. The screen is used to cover the system while the keyboard is installed flatly on the system unit. They could
be carried about like a box when closed after operation and can be operated in vehicles while on a journey.

Notebook Computer

This is like laptop computers but smaller in size. Though small, it comprises all the components of a full system.

Palmtop Computer

Palmtop computer is far smaller in size. All the components are complete as any of the above but made smaller so that it can be held on the palm.

Uses of Personal Computers

1. Personal computers can perform the following functions: 
2. Can be used to produce documents like memos, reports, letters and briefs. 
3. Can be used to calculate budget and accounting tasks 
4. It can analyze numeric function 
5. It can create illustrations 
6. Can be used for electronic mails 
7. Can help in making schedule and plan projects. 
8. It can assist in schedules and plan projects. 
9. It can assist in searching for specific information from lists or from reports. 

Advantages of Personal Computers

1. Computer is versatile; it can be used in any establishment. 
2. Has faster speed for processing data. 
3. Can deal with several data at a time 
4. Can attend to several users at the same time, thereby able to process several jobs at a time.
5. Capable of storing several data. 
6. Operating of Computer is less fatigue 
7. Network possible, that is linking of two or more computers together. 

Disadvantages of Personal Computers

1. Computer is costly to maintain. 
2. It is very fragile and complex to handle 
3. It requires special skill to operate 
4. With the invention and innovation everyday, computer suffers from being obsolete. 
5. It can lead to unemployment when used mostly in less Developed Countries. 
6. Some computers can not function properly without the aid of cooling system e.g. 
7. air-condition or fan in some locations. 

Mini Computers

The Mini Computers have memory capacity in the range 128K bytes to 256 Kbytes and are also not expensive but reliable and smaller in size compare to mainframe. It was first introduced in 1965; when DEC (Digital Equipment Corporation) built the PDP – 8. Other Mini Computer includes WANG VS.

Mainframe

The Main Frame Computers often called number crunches have memory capacity of the order of 4 Kbytes and they are very expensive. They can execute up to 100MIPS (Meanwhile Instructions Per Second). They have large systems and are used by many people for a variety of purpose.

Conclusion

Computers are classified based on three major criteria namely size, type of signal being processed and purpose. The classification adopted at any point in time depends on the issues involved. For instance, if our goal is to process different kinds of signals or to accept one type of signal and convert to another form of signal, we should look in the realm of analog or digital or even the hybrid computers. This of course, calls for a converter such as Analog to Digital Converter or Digital to Analog Converter as the case may be.