• Analog Computers
- Analog computers are used to process analog data. Analog data is of continuous nature and which is not discrete or separate. Such type of data includes temperature, pressure, speed weight, voltage, depth etc. These quantities are continuous and having an infinite variety of values.
- It measures continuous changes in some physical quantity e.g. The Speedometer of a car measures speed, the change of temperature
is measured by a Thermometer, the weight is measured by Weights machine. These computers are ideal in situations where data can be accepted directly from measuring instrument without having to convert it into numbers or codes.
- Analog computers are the first computers being developed and provided the basis for the development of the modern digital computers. Analog computers are widely used for certain specialized engineering and scientific applications, for calculation and measurement of analog quantities. They are frequently used to control process such as those found in oil refinery where flow and temperature measurements are important. They are used for example in paper making and in chemical industry. Analog computers do not require any storage capability because they measure and compare quantities in a single operation. Output from an analog computer is generally in the form of readings on a series of dial (Speedometer of a car) or a graph on strip chart.

• Digital Computers
- A Digital Computer, as its name implies, works with digits to represent numerals, letters or other special symbols. Digital Computers operate on inputs which are ON-OFF type and its output is also in the form of ON-OFF signal. Normally, an ON is represented by a 1 and an OFF is represented by a 0. So we can say that digital computers process information which is based on the presence or the absence of an electrical charge or we prefer to say a binary 1 or 0.
- A digital computer can be used to process numeric as well as non-numeric data. It can perform arithmetic operations like addition, subtraction, multiplication and division and also logical operations. Most of the computers available today are digital computers. The most common examples of digital computers are accounting machines and calculators.
The results of digital computers are more accurate than the results of analog computers. Analog computers are faster than digital. Analog computers lack memory whereas digital computers store information. We can say that digital computers count and analog computers measures.

• Hybrid Computers
- A hybrid is a combination of digital and analog computers. It combines the best features of both types of computers, i-e. It has the speed of analog computer and the memory and accuracy of digital computer. Hybrid computers are used mainly in specialized applications where both kinds of data need to be processed. Therefore, they help the user, to process both continuous and discrete data. For example a petrol pump contains a processor that converts fuel flow measurements into quantity and price values. In hospital Intensive Care Unit (ICU), an analog device is used which measures patient’s blood pressure and temperature etc, which are then converted and displayed in the form of digits. Hybrid computers for example are used for scientific calculations, in defense and radar systems.

• General Purpose computer
- A general-purpose computer is one that, given the appropriate application and required time, should be able to perform most common computing tasks.  
Personal computers, including desktops, notebooks, smartphones and tablets, are all examples of general-purpose computers. The term is used to differentiate general-purpose computers from other types, in particular the specialized embedded computers used in intelligent systems.

• Turnkey System
- A computer system that is set up or designed to satisfy all the customer's needs. For example, many companies will set up a turnkey system for its employees, which has all of the necessary hardware and software for the employee to begin working. Because many consumers need to install software or customize their computer, most computers are not considered a turnkey system.

• Micro computer
- Micro Computer is a small computer.  personal computers are equivalent to the microcomputer. Mainframe and Mini Computer is ancestor of microcomputer. Integrated Circuit fabrication technology reduces the size of Mainframe and Minicomputer.
Technically, a microcomputer is a computer in which the CPU (central processing unit, the brains of the computer) is contained on one single chip, a microprocessor, input/output devices and storage (memory) unit. All these components are important for a proper working of microcomputer.

• Types of Micro Computer
- Most workstations are also types of micro computer, for the same reason, although some personal computer is as fast as the fastest workstation. And a computer used by more than one person (a multi-user computer) is still a microcomputer as long as it has a microprocessor for its CPU.

* Notebook
- Notebook is the smallest microcomputer, which can be ultra-mobile3 inches thick with less than 3 pounds lightweight and smaller than a briefcase, allow for easy setup in a room. A notebook can be effectively connected to the Internet ISP via a cable or Wi-Fi.

* Laptop
- Laptop microcomputer is bigger than the notebook computer powered by a battery and designed for low power consumption, which can be smaller than a briefcase. Although laptops and desktop computers have same capabilities. A laptop also has a thin display screen with attached keyboard and a touchpad used for navigation.

* Desktop
- Desktops are personal computers and bigger than notebooks and laptops. These microcomputers consist of the system unit, keyboard and monitor. Desktop microcomputers are cheaper than laptops or notebooks. Unlike a notebook ,which is ultra-mobile, a desktop microcomputer stay at one location. The desktop microcomputers are more reliable than notebooks and laptops and easy to repair.

* Mini Computer
- A minicomputer is also known as mini. It is a class of small computers that was introduced into the world in the mid-1960s. A minicomputer is a computer which has all the features of a large size computer, but its size is smaller than those. A minicomputer lies between the mainframe and the microcomputer because its size is smaller than the former one and larger than the latter one. A minicomputer is also called as a mid-range computer. Minicomputers are mainly multi-users systems where more than one user can work simultaneously. Mini computer examples: IBM’s AS/400e, Honeywell200, TI-990
Minicomputer can support multi-users at a time or you can say that minicomputer is a multiprocessing system. Also, the power of processing of minicomputers is not larger than the power of mainframe and supercomputers. These minicomputers can do time-sharing, batch processing, and online processing.

The types of minicomputer are- tablet PC, Desktop minicomputers, cell phones, notebooks, etc.

* Mainframe Computer
- Mainframe computers can store huge amount of data. They are large in size and memory, power and expensive. These machines are capable to different operating system on the same time and support time sharing and virtual memory. Universities, banking institutions, stock exchanges, insurance companies are some examples of using mainframe servers for maintaining students’ data, ATM transactions, financial transactions, clients and employees’ records.
- The main difference between supercomputer and mainframes is that supercomputer has a speed of calculations and mostly used for space scientific and engineering related problems i.e. data crunching while mainframe servers are used for transaction process.

• Modern mainframes Computers
1. IBM zSeries
2. System z9
3. System z10 servers

• Supercomputer
- The term “super computer” is considered the most powerful computers in performance and processing. Supercomputers are capable to solve immense mathematical calculations, scientific problems and hence it is called number crunchers. They are difficult to design and need teamwork research and development.

Uses of Supercomputer
Theses monster machines are capable to play their role in the field of weather forecasting, quantum mechanics and physical simulation (spaceship aerodynamics and testing of nuclear weapons. Another important application of supercomputer is oil exploration. A program can simulate areas where oil is likely to be found and can predict costs and methods of findings and retrieving oil.

Examples of Some Supercomputer
1. IBM Roadrunner
2. Trinity by Cray Inc.
3. IBM Sequoia