Computers can be classified into three major classes based on the mode of data representation used.
1. Analog Computers
2. Digital Computers
3. Hybrid Computers
1. Analog Computers
1.An analog computer is a form of computer that uses continuous physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved.
It operates by measuring rather than counting.
It uses continuous signals as input.
Examples: Thermometer, Speedometer etc.
2. Digital Computers
1. A computer that performs calculations and logical operations with quantities represented as digits, usually in the binary number system
2. These are the systems that are computationally complete and capable of solving all of the problems that can be solved algorithmically.
Examples: Desktop, laptop etc
Hybrid Computers
1. A combination of computers those are capable of inputting and outputting in both digital and analog signals. A hybrid computer system setup offers a cost effective method of performing complex simulations.
2. It use both types of signals – analog as well as digital – as input.
3. Mostly used with process control equipments in continuous production plants e.g., oil refineries, Areas of application are nuclear power plants, mines, intensive care units of hospitals (ICUs), chemical process plants etc.
Classification of Digital Computers
The digital computers that are available nowadays vary in their sizes and types. The computers are broadly classified into four categories based on their size and type
1. Microcomputers
2. Minicomputers
3. Mainframe computers
4. Supercomputer
1. Microcomputers
Microcomputers are small, low-cost and single-user digital computer. They consist of CPU, input unit, output unit, storage unit and the software.
IBM PC based on Pentium microprocessor and Apple Macintosh are some examples of microcomputers. Microcomputers include desktop computers, notebook computers or laptop, tablet computer, handheld computer, smart phones and netbook,
(a) Desktop Computer or Personal Computer (PC) - It is the most common type of microcomputer. It consists of three units—keyboard, monitor, and a system unit containing the CPU, memory, hard disk drive, etc. It is not very expensive and is suited to the needs of a single user at home, small business units, and organizations. Apple, Microsoft, HP, Dell and Lenovo are some of the PC manufacturers.
(b) Notebook Computers or Laptop - They are portable and have all the features of a desktop computer. The advantage of the laptop is that it is small in size, can be carried anywhere. Laptops can be placed on the lap while working. Laptops are costlier than the desktop machines.
(c) Netbook - These are smaller notebooks optimized for low weight and low cost, and are designed for accessing web-based applications. Netbooks deliver the performance needed to enjoy popular activities like streaming videos or music, emailing, Web surfing or instant messaging.
(d) Tablet - Tablet Computer has features of the notebook computer but it can accept input from a stylus or a pen instead of the keyboard or mouse. It is a portable computer. Tablet computer are the new kind of PCs.
(e) Handheld Computer or Personal Digital Assistant (PDA) - It is a small computer that can be held on the top of the palm. It is small in size. PDA uses a pen or a stylus for input, Instead of the keyboard. They have a limited memory and are less powerful. PDAs can be connected to the Internet via a wireless connection. Example Casio and Apple are some of the manufacturers of PDA.
(f) Smart Phones - These are cellular phones that function both as a phone and as a small PC. They may use a stylus or a pen, or may have a small keyboard. They can be connected to the Internet wirelessly. They are used to access the electronic-mail, download music, play games, etc. Blackberry, Apple, HTC, Nokia and LG are some of the manufacturers of smart phones.
2. Minicomputers
Minicomputers are digital computers, generally used in multi-user systems. Minicomputers are mainly used as small or midrange servers operating business and scientific applications. They have high processing speed and high storage capacity than the microcomputers. Minicomputers can support 4–200 users simultaneously. The users can access the minicomputer through their PCs or terminal. Example Digital Alpha, Sun Ultra.
3. Mainframe Computers
Mainframe computers are multi-user, multi-programming and high performance computers. They operate at a very high speed, have very large storage capacity and can handle the workload of many users. Mainframe computers are large and powerful systems generally used in centralized databases. Computers with large storage capacities and very high speed of processing (compared to mini- or microcomputers) are known as mainframe computers. They support a large number of terminals for simultaneous use by a number of users like ATM transactions. They are also used as central host computers in distributed data processing system. Mainframe computers are used in organizations like banks or companies, where many people require frequent access to the same data.
Examples: - IBM 370, S/390.
4. Supercomputers
Supercomputers are the fastest and the most expensive machines. They have high processing speed compared to other computers. The speed of a supercomputer is generally measured in FLOPS (Floating point Operations per Second). Some of the faster supercomputers can perform trillions of calculations per second.
Supercomputers are used for highly calculation-intensive tasks, such as, weather forecasting, climate research (global warming), molecular research, biological research, nuclear research and aircraft design. They are also used in major universities, military agencies and scientific research laboratories.
Some examples of supercomputers are IBM Roadrunner, IBM Blue gene and Intel ASCI red. PARAM is a series of supercomputer assembled in India by C-DAC (Center for Development of Advanced Computing), in Pune. PARAM Padma is the latest machine in this series. The peak computing power of PARAM Padma is 1 Tera FLOP (TFLOP).
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