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    As technology advances, computers are quickly becoming more powerful. Those days are gone. Computers come in all shapes and sizes now, from big and scary to small and cuddly. Sometimes you cant even tell if something is a computer or not. Strictly speaking, any device that can take data, process it according to specific instructions, and then output the results is a computer. A definition that broad doesnt clarify much, however.

In the interests of making things a bit simpler, most computers can be divided into several categories. Familiar types include supercomputers, mainframes, workstations, servers, and desktop computers. Each has a different role in its little computer life.

Based on sizes, computers can be categorized into:

               I.      Supercomputers

             II.      Mainframes

            III.      Minicomputers

        IV.      Microcomputer



Physical size

Number of instructions executed per second

Number of simultaneously connected users

General price tag


Personal Computer (microcomputer)


Fit in your hand or your desk


Up to 400 million


One stand-alone or networked


Several thousand dollars or less



Small cabinet


Thousands to millions


Two to 4,000

$5,000 -$150,000



Partial room to a full room of equipment




Hundreds to thousands

$300,000-several million dollars



Full room of equipment


Millions to billions


Hundreds to thousands


Several million dollars and up




Seymour Cray (FATHER OF SUPERCOMPUTER) is intimately associated with the

history of supercomputers, having designed many of the world's fastest computers throughout the 1960s, 1970s, and 1980s for Control Data Corporation and Cray Research. Supercomputer are the brainiest computers that many people once pictured when they thought of the word computer in all its Orwell Ian might. Supercomputers are huge, incredibly expensive, extremely fast, and stunningly complex machines used for large-scale scientific modeling. Capable of processing more than 64 billion instructions in a single second, supercomputer are used for applications requiring complex, sophisticated mathematical calculations. For example, a supercomputer would be used for



      Weather forecasting

      Nuclear energy research

      Petroleum exploration                                                        

      Weapons research                                                                     

      Aircraft designs


Their memory hierarchy is very carefully designed to ensure the processor is kept fed with data and instructions at all timesin fact, much of the performance difference between slower computers and supercomputers is due to the memory hierarchy design and component. Their I/O systems tend to be designed to support high bandwidth, with latency less of an issue, because supercomputers are not used for transaction processing.

Vector processing techniques were first developed for supercomputers and continue to be used in specialist high-performance applications. Their operating systems, often variants of UNIX, tend not to be as sophisticated as those for smaller machines, since supercomputers are typically dedicated to one task at a time rather than the multitude of simultaneous jobs that makes up the workload of smaller devices.



The speed of a supercomputer is generally measured in FLOPS (floating point operations per second); this measurement ignores communication overheads and assumes that all processors of the machine are provided with data and are working at full speed. As of early 2002, the fastest supercomputer is the Earth Simulator at the Yokohama Institute for Earth Sciences. It is a cluster of 640 custom-designed 8-processor vector processor computers based on the NEC SX-6 architecture (a total of 5120 processors). It uses a customized version of the UNIX operating system.



As technology advance, computers are quickly becoming more powerful. The lines of category become blur and unclear but generally, computers can be classified based on their sizes and processing power.

A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe. The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.

Supporters claim that mainframes still house 90% of the data major businesses rely on for mission-critical applications, attributing this to their superior performance, reliability, scalability, and security compared to microprocessors

      Mainframes are so named because they were the first built by placing computer components on a chassis, or main frames .

      Generally found in a special computer room where environmental such as temperature, dust, and humidity are controlled.

      Have primary storage measured in megabytes or gigabytes.

      Can process data at million instructions per second (MIPS). 

      More than 1,000 remote terminals or workstations connected to mainframes. 

      Still used by large corporations, such as banks that are very large amounts of data to process on big databases.

      Would be used as the main computer.

      The price of these large systems can very from several hundred thousand to many millions off dollars. Used for processing vast amount of data quickly, such as bank (ATM), insurance companies, manufacture, airlines companies, aerospace companies doing complex aircraft design, Internets servers etc.

A key characteristic of large computer is that they are designed for multiple users. For examples, many reservations clerks could be accessing the same computer at the same time to make reservation for waiting customers.

   Examples: IBM 3090, ICL 39 SX series. 



A computer built between about 1963 and 1987, smaller and less powerful than a mainframe, typically about the size and shape of a wardrobe, mounted in a single tall rack.

Short word lengths of 8 to 32 bits, limited hardware and software facilities and small physical size characterized minicomputers. Their low cost made them suitable for a wide variety of applications such as industrial control, where a small, dedicated computer, which is permanently assigned to one application, is needed. In recent years, improvements in device technology have resulted in minicomputers that are comparable in performance to large second-generation computers and greatly exceed the performance of first generation computers.

The processor was typically built using low integration logic integrated circuits - TTL or maybe ECL, thus distinguishing it from a microcomputer which is built around a microprocessor - a processor on a single (or maybe a few) ICs.

DEC's PDP-1 was the first minicomputer and their PDP-11 was the most successful, closely followed (in both time and success) by the VAX (which DEC called a "super minicomputer").





Microcomputers is much more smaller than minicomputer. Even though it small and cheap but has fairly limited power. In other sense more micro is personal computer to work with at a time because it user friendly. That can be defined as computer with storage capacity 256 kilobytes to several megabytes. There are many different types of computer - used for many different jobs. Here are some of the popular types of computer that you can find in use today.



A pocket computer has to have small, light batteries that last a long time so that the whole computer is light and small enough to be carried around in someone's pocket.
These computers have special operating systems suited to pocket computers.
One problem with small computers is that they don't have full-sized keyboards attached. Both of the computers in these pictures use special pens and touch-sensitive screens to enter data as well as a number of small buttons or keys.



The person using a laptop should be able to run all the same software on the laptop as runs on larger, desktop computers as laptop computers have the same types of operating system as desktop ones. Modern laptops can have floppy drives, CD-ROM drives and CD re-writers, and even DVD drives. They often have full-sized, or near-full-sized keyboards and a mouse or a touch-sensitive mouse pad. The screen is usually a large Liquid Crystal Display (LCD). The main advantage of a laptop is that the person using it can have all the programs and data from their desktop computer on a portable computer.



The latest operating system for the Apple Mac (in 2002) is OS X. When people talk about PCs they usually mean and IBM-compatible' computer based on an Intel (or similar) microprocessor. The most common operating system for the PC is Microsoft Windows (latest version Windows XP) although other operating systems are available (e.g. Linux). These are very popular computers. They are designed to be used on a desk or table with a separate keyboard and mouse for input