---

These days, computers are available in many sizes and types. One can have a computer that can fit in the palm of the hand to those that can occupy the entire room. Some computers are designed to be used by a single user only, whereas some computers can handle the needs of many users simultaneously. Computers also differ based on their data processing abilities. In general, they can be classified according to purpose, data handling and functionality. The classification of computers according to purpose and data handling only are discussed as follows:

Classification According to Purpose

Computers are designed for different purposes. According to the need, they can be classified into two categories, which are described as follows:

General purpose computers:

As the name suggests, they are designed to perform a range of tasks. These computers have the ability to store numerous programs. These machines can be used for various applications, ranging from scientific as well as business purpose applications. Even though such computers are versatile, they generally lack in speed and efficiency. The computers that are used in schools and homes are general purpose computers.

Specific purpose computers:

They are designed to handle a specific problem or to perform a single specific task. A set of instructions for the specific task is built into the machine. Hence, they cannot be used for other applications unless their circuits are redesigned, that is, they lack versatility. However, being designed for specific tasks, they can provide the result very quickly and efficiently. These computers are used for airline reservations, satellite tracking and air traffic control.

Classification According to Type of Data Handling Techniques

Different types of computers process the data in a different manner. According to the basic data handling techniques, computers can be classified into the following three categories:

Analog computers:
A computing machine that operates on data in the form of continuously variable physical quantities is known as ‘analog computer’. These computers do not deal directly with the numbers. They measure continuous physical magnitudes (such as temperature, pressure and volt-age), which are analogous to the numbers under consideration. For example, the petrol pump may have an analog computer that converts the flow of pumped petrol into two measurements – the quantity of petrol and the price for that quantity. Analog computers are used for scientific and engineering purposes. One of the characteristics of these computers is that they give approximate results since they deal with quantities that vary continuously. The main feature of analog computers is that they are very fast in operation as all the calculations are done in parallel mode. It is very easy to get graphical results directly using analog computer. However, the accuracy of analog computers is less.

Digital computers:
A computer that operates with information, numerical or otherwise, represented in a digital form is known as ‘digital computer’. Such computers process data (including text, sound, graphics and video) into a digital value (in 0s and 1s). In digital computers, analog quantities must be converted into digital quantity before processing. In this case, the output will also be digital. If analog output is desired, the digital output has to be converted into analog quantity. The components, which perform these conversions, are the essential parts or peripherals of the digital computer. Digital computers can give the results with more accuracy and at a faster rate. The accuracy of such computers is limited only by the size of their registers and memory. The desktop PC at the home is a classic example of digital computer.

Hybrid computers:
They incorporated the measuring feature of an analog computer and counting feature of a digital computer. For computational purposes, these computers use the analog components and for the storage of intermediate results, digital memories are used. In order to bind the powers of analog and digital techniques, analog to digital and digital to analog, the hybrid computers comprehensively use converters. Such computers are broadly used for scientific applications, various fields of engineering and in industrial control processes.

Classification of computers according to functionality

Based on physical size, performance and application areas, computers can be generally divided into four major categories, namely, micro, mini, mainframe and super computers. All of these are described as follows:

Micro Computers
A micro computer is a small, low-cost digital computer, which usually consists of a microprocessor, a storage unit, an input channel and an output channel, all of which may be on one chip inserted into one or several PC boards. The addition of a power supply and connecting cables, appropriate peripherals (keyboard, monitor, printer, disk drives and others), an operating system and other software programs can provide a complete micro computer system. The micro computer is generally the smallest of the computer family. Originally, these were designed for individual users only, but nowadays they have become powerful tools for many businesses that, when networked together, can serve more than one user. IBM-PC Pentium 100, IBM-PC Pentium 200 and Apple Macintosh are some of the examples of micro computers. Micro computers include desktop, laptop and hand-held models, such as personal digital assistants (PDAs).

Mini Computers
A mini computer is a small digital computer that normally able to process and store less data than a mainframe but more than a micro computer, while doing task less rapidly than a mainframe but more rapidly than a micro computer. These computers are about the size of a two-drawer ?ling cabinet. Generally, they are used as desktop devices that are often connected to a mainframe in order to perform the auxiliary operations.
Mini computer (sometimes called a ‘mid-range computer’) is designed to meet the computing needs of several people simultaneously in a small to medium-sized business environment. It is capable of supporting from 4 to about 200 simultaneous users. It serves as a centralized storehouse for a cluster of workstations or as a network server. Mini computers are usually multi-user systems so these are used in interactive applications in industries, research organizations, colleges and universities. They are also used for real-time controls and engineering design work. Some of the widely used mini computers are PDP 11, IBM (8000 series) and VAX 7500.

Mainframes
A mainframe is an ultra-high performance computer made for high-volume, processor-intensive computing. It consists of a high-end computer processor, with related peripheral devices, capable of supporting large volumes of data processing, high performance online transaction processing and extensive data storage and retrieval. Normally, it is able to process and store more data than a mini computer and far more than a micro computer. Moreover, it is designed to perform at a faster rate than a mini computer and at even more faster rate than a micro computer. Mainframes are the second largest (in capability and size) of the computer family, the largest being the super computers. However, they can usually execute many programs simultaneously at a high speed, whereas super computers are designed for a single process.
Mainframes allow its user to maintain a large amount of data storage at a centralized location and to access and process this data from different computers located at different locations. They are typically used by large businesses and for scientific purposes. Some examples of mainframe are IBM’s ES000, VAX 8000 and CDC 6600.

Super Computers
Super computers are the special purpose machines that are specially designed to maximize the numbers of FLOPS (Floating Point Operation per Second). Any computer below one giga?op/sec is not considered a super computer. It has the highest processing speed at a given time for solving scientific and engineering problems. Essentially, it contains a number of CPUs that operate in parallel to make it faster. Its processing speed lies in the range of 400–10,000 MFLOPS (Millions of Floating Point Operation per Second). Due to this feature, super computers help in many applications including information retrieval and computer-aided design.
A super computer can process a great deal of data and make extensive calculations very quickly. It can resolve complex mathematical equations in a few hours, which would have taken many years when performed using a paper and pencil or using a hand calculator. It is the fastest, costliest and most powerful computer available today. Typically, super computers are used to solve multi-variant mathematical problems of existent physical processes, such as aerodynamics, metrology and plasma physics. They are also required by the military strategists to simulate defense scenarios. Cinema technicians use them to produce sophisticated movie animations. Scientists build complex models and simulate them in a super computer. However, super computer has a limited broad-spectrum use because of its price and limited market. The largest commercial uses of super computers are in the entertainment/advertising industry. CRAY-3, Cyber 205 and PARAM are some well-known super computers.

---