CLASSIFICATION OF DIGITAL COMPUTER 

                                                          PERSONAL COMPUTER

Computers for personal use come in all shapes and sized from tiny personal digital assistant to hefty personal computer towers . More specialized models are announced each week trip planners, expense account pads language translators.....
                                                         MAIN FRAME COMPUTER 

The main frame is the workhorse of the business world .A main frame is the heart of a network of computer or terminals which allows hundreds of people to work at the same time on the same data. It requires a special environment cold and try.
                                                          SUPER COMPUTER 

The super computer is the top of the heap in power and expense . These are used for jobs that take massive amounts of calculations like weather forecasting engineering design and testing serious decryption economic forecasting etc.
                                                          MINI COMPUTER 

The mini computer has become less important since the personal computer has gotten so power full on its own .In fact the ordinary new personal computer is much more powerful than mini computers used to be originally this size was developed to handle specific tasks like engineering and CAD calculations which tended  to tie up the main frame computers .


A  network is a set of computer which are linked together on a permanent basis . This can dean two computers cabled together on the same desk or thousands of computer across the world.


A lan is a local area network .This would include networks where the computers are relatively close together.. So local Area Network would be within the same office a single building or sevral buildings close together .

The graphic at the right shows two buildings with 4 departments connected as a local Area Network .

        A wan is a Wide Area Network which would be all networks too large to be Lans .  There doesn't seem to be a clear line between the two designation .  A wide Area Network would be most useful for large companies with offices or factories in widely separated areas like Microsoft IBM Ford etc..

There are a number of ways that computers can be connected together to form networks.
Each device in the network whether its a coputer printer scanner or whatever is called a node .


  The star pattern connects everything to one host which is the computer that handles the network tasks and holds the data.  All communications between computers go through the host. This configuration is good for businesses that have large amounts of rapidly changing data like banks and airline reservation offices.

Advantages :
    Gives close control of data . Each pc sees all the data User seen up to data data always. If a computer other than the host fails no other computer is affected .
Disadvantages :

   If host computer or its software goes down the whole network is down.


The buspattern connects the computer to the same communications line . Communications goes both directions along the line. All the computers can communicate with each other without having to go through the server.

Advantages :

     Any one computer or device being down does not affect the others.

     Can't connect a large number of computer this way It's physically difficult to run the one communications line over a whole building for example.

Ring :

   The ring pattern connects the computers and other devices one to the othe rin a circle . There is no central host computer  that holds all the data . Communication flows in on edirection around the ring , This configuraton is good when the processing of data can be done on the local PC.


      Requires less cabling and so is less expensive.

Disadvantages; If one node goes down it takes down the whole network.


      Networks can be connected to each other too There are difficulties in dong so however . A combination of sofrware and hardware must be used to do the job.
A gateway connects netword of different kinds like connectiong a network of PCs to a main frame network .This can be complex!

A  bridge connects networks of the same type . This job is simple .
A router connects se
veral networks / A router is smart enough to pock the right path for communications traffic Of there is a partial failure of the network a router looks for an alternate route.