Analog computers : Analog computers are those which work on the basis of continous measurement of physical quantities such as preassure, voltage, current, temprature, length etc. and convert them to numeric values. They are used mainly for scientific and engineering purposes because they deal with quantities that vary constantly. They give approximate results.

• For example :

- Thermometer
- speedometer
- Voltmeter etc.

It is also used in oil refineries where flow measurements and temprature measurements are important.

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Digital Computers : Digital computers are those which represent data in terms of discrete numbers and process data using standards arithmatic operations. These computers directly operates on numbers which is essentianlly in binary or two state state format. There can be special purpose digital computer which can be fixed permanantly into the machine.

• For example :

Processors that are installed in automobiles to control ful breaking system. General purpose digital computer can be used in different application since they can share different sets of instructions and programmes.

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Hybrid Computers : Analog and Digital computers intermingle with each other to make a hybrid computers. In other words, we can say that features of analog and digital computers are combined to create a hybrid computer computing system.

• For example :

- Flight simulators for training airplane pilots
- Petroleum distilation
- Monentry systems
- Missile guidance computers etc.

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Micro Computers : Microcomputers are at the lowest end of computer range. Desktop computers like PC/XT, PC/AT, IBM PC, Apple's Macintosh etc. all fall into the category of micro computers. Micro computer are typically single user systems. They have small to medium data storage capacities. Inside a micro computer, the arithmatic and control unit are combined on a single chip called microprocessor. These are used in various fields such as :

- Accounting
- Project management
- Teaching
- entertainment etc.

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Mini Computers : Mini computers have more powerful than micros and can support several users. They are larger in size and cost more than micro computer. They have larger storage capacity and can process or operate data at higher speeds. They are basically developed for use in process control system and can handle common appplications also. They can support faster peripheral devices like high speed printers and can also communicate with main frames. They are used to control and monitor production process, to meet instructional needs of the colleges etc. They can also be used as serves in LANS

• For example :

- VAX II
- Digital equipment's PDP etc.

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Main Frames : Mainframes are more powerful than minis. The earliest computers were called mainframes due to their large size. Mainframes operate at very high speed, having very large storage capacities and can support hundred of users. Because they can process large amounts of datavery quickly, they are used by large organisations where the records of thousands of employees have to be processed. They are also used to manage large centralized databases. They also act as hosts of large national and international communication networks. They are used as controlling needs in WANs.

• For example :

- IBM 300 Series
- UNIVAC 1180
- ICL 39 series
- CDC cyber series etc.

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Super Computers : Super computers are at the apex of computer range. They are the fastest and the most expensive machines, and are considered a national resource. Super computer allow faster processing by using multiple processors and superior techniques are used for complex tasks which require a lot of computational power.
          These are used for weapons designing as well as commercial purposes like designing automobiles, for better protection etc. These are also used in weather forcasting, biomedical resarch and aircraft design etc.
          The tradition design of a single processor handling data and instructions in a single streams is called " Von - Neuman design ". They have several ALUs and each have a specified operation.
          There are less than 500 conventional supercomputers in the world.

• For example :

- Paragon from Intel Corporation U.S.A.
- Supercomputers Systems Divison from nCube U.S.A
- 2S from nCube
- Parani from C-DAC India
- CRAY XMP-24 etc.

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Workstations : Workstaions is an inexpensive and very powerful machine used by engineers, scientist and other professors who need to process a lot of data. People who need to execute complicated programs and display both work in progress & output, graphically also make use of these workstations. Workstations provides processor speed about 10 times of PC's. These are extensively used for computer graphics, computer aided design (CAD) etc. Graphic workstations can manipulate lines, curves, figures and engineering or architectural designs efficienctly.

Routers : A router is a device used to connect networks that use different architectures and protocols. They can switch and transfer information packets across multiple networks. This process is called routing. They can determine the best path for sending data and flitering broadcast traffic to the local segment. Routers can not link to remote computers. Routers can link segments that use different data packaging and media access schemes.

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Gateways : Gateways make communicate possible between systems that use different communication protocols, data formatting structures, languages and architechures. Gateways repackage data going from one system to another. Gateways are usually dedicated servers on a network and are task specific.

Analog Computers	Digital Computers
1. It represents continous measurement of physical quantities.   Example :       Voltage, preassure etc.	1. Digital Computers represent numbers by discrete coded patterns.
2. Accuracy is limited.	2. Unlimited accuracy.
3. Represent physical or mathematical quantities.	3. Represents numbers, letters and other symbols.
4. Distinct elements used for operation.	4. Identical elements are used in sequence.

History : In 1969, the department of defense of USA started a network called ARPAnet ( Advanced Resarch Projects Administration network ). Firstly it started in a modest way but later to share the software and hardware resources, the military allowed universities to join the network, from where the students caught up with it and developed much of the software, giving birth to now so very papular INTERNET.

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What is Internet : Internet is a interconnection between several computers of different types belonging to various networks all over the globe. It is a network of networks.
      The kind of colossal powers which internet gives over machine is mind-boggling. To send or recieve data within a matter of seconds to someone placed beyond the pacific was unthinkable before the advent of the Internet. Internet represents that transformation and evaluation of the entire information age. It is due to these factors that people all over the globe have recognised internet as their latest development tool. The internet is making a major impact on the information technology industry. Major companies like Microsoft, AT & T, INTEL etc. have reworked their business stratergies vis-a-vis Inernet.

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Advantages of Internet : The internet is simuntaneously a :

• Network : Organizations can use the internet to link their offices and employees, turning the internet into a virtual private network.

• Medium : The internet serves as a communication channel for anybody dealing with product marketing to corporate communications.

• Market : The internet is a vast virtual market place where you can advertise and even order products from the market.

• Transaction Platform : Internet allows you to complete your business transactions in the market place (ie) you complete your financial transactions online while linked directly to your suppliers, customers or financial institutions.
        The internet is an information super highway and has compressed the world into a cyber colony. Though there are no set rules for managing and accessing data over the internet and a society called Internet Society (ISOC) exists and is working towards bringing order and direction to such vast undertaking.

Intranets : Intranets are information networks that are local to an organization. They make use of same internet technologies to share data within an organization. If Internet server software is installed on the servers connected by LAN, we can make use of internet technologies to share data within our organization. For this reason, Internet are sometimes referred to as Internet Web. Intranets uses internet technology and permits an organization to define itself as whole entity, a group where everyone knows his/her roles.

        Intranets can be : -

• Decision Making Tool
• Learning Organizational Tool
• Communication Tool
• Experts Tool
• Customer Tool
• 21st Century Telephone