Super computers are the fastest and largest computers, have large memories and high processing speeds up to billion instructions per second. Has ability to recover automatically from failures (fault tolerance). Super computers have multiple processors that process multiple instructions at a time known as parallel processing.

A mainframe is a large, general-purpose computer with a large memory and excellent processing capabilities. They are ideal for transaction processing, financial applications payrolls, investment analysis, weather forecasting reservations and other applications that require massive computations and large scale processing.

Minicomputers are small workgroup systems, yet powerful multi-user systems with excellent memory capabilities and processing speeds. Minicomputers are widely used in distributed environment and are more scalable.

Workstations are between mini and microcomputers. They are used by individuals or groups. They are equipped with a number of productivity tools that increase their efficiency. Engineers, designers, architects and film industry animators use workstations heavily.

Microcomputers are known as personal computers (PCs), have completely changed the business. PC is compact, powerful and versatile machine.

Laptops and notebooks provide mobile computing technology. These are battery operated. They are equipped with powerful microprocessors, graphic capabilities, adequate memory and mouse driven input. Can be connected to Internet and LAN. The portability of notebooks and laptops has increased the productivity of those who travel extensively. Sales representatives can access corporate database and retrieve information almost instantaneously.

Hand held computers are smaller than notebooks primarily used to collect field data.

Pen based computing refers to portable computers that use an electronic writing pad. When the user writes on the pad, the writing is converted into digital input and stored in a file in the computer.

A computer is a data processing machine that process data and provides meaningful information. It processes information with astonishing speed and accuracy. Computers process information by helping to create it and by displaying it, storing it, reorganising it, calculating with it, and communicating it to other computers. Computers can process numbers, words, still pictures, moving pictures, and sounds. The most powerful computers can perform tens of billions of calculations per second.

Almost all computers are electronic digital computers. They are electronic in their use of electric current (a flow of electric charge) to carry information. They are digital in that they process information as units of electric charge representing numbers. The word digital means having to do with numbers.

Analog computer is a device that solves problems by working directly with a physical quantity, such as weight, voltage, or speed, rather than with digits that represent the quantity. The computers solve problems by measuring one quantity in terms of another quantity.

In a problem involving water pressure and water flow, for example, electrical voltage might serve as an analogue (likeness) for the water pressure, and electric current for the water flow. Many familiar devices, including speedometers, thermometers, and thermostats, operate on the same basic principle as analog computers. For example, a thermometer measures temperature in terms of the length of a thin line of liquid in a tube. An analog computer presents output data in a continuous form, often as a position on a scale. In some cases, the data are displayed as electrical signals on an instrument called an oscilloscope.

Digital computers represent data as numbers or separate units. Digital computer can accurately represent data using as many positions and numbers as necessary. Analog computers derive all their data from some form of measurement. Viz. Length of an object, angles created by two lines, temperature recorded on thermometer.