According to size the computer are classified into four major type;

• Microcomputers
• Minicomputers
• Mainframe Computers
• Super Computers

Microcomputers

Desktop computers, laptops, gaming consoles, sound and navigation system of a car, personal digital assistant (PDA), tablets and smartphones are all types of microcomputers.The microcomputers are widely used and the fastest growing computers. These computers are the cheapest among the other three types of computers.The microcomputers are specially designed for general purpose usage life entertainment, education, and work purposes. Desktop computer, workstation, laptop, plamtop. tablet, smart phones are some of the different microcomputers.some main characteristics of desktop computers:

• Fast speed and accuracy
• Small in size
• Easy to operate
• Easy to move
• Cheaper
• We can use desktop computers as a single user and multi-user environment

Minicomputers

Minicomputers also called as mid-range servers, are more powerful computers than microcomputers in terms of processing power and capabilities. Minicomputers are mainly multi-user systems where many user simultaneously work on the systems. Minicomputers posses greater storage capacity and larger memories as compared to microcomputer. These are even capable of handling more input/output devices. These are popular among students, professionals and home users due to small size, low price and low maintenance. PDP-11,VAX, 7500 MAGNUM are some example of mini computer.

Mini Computers are medium sized computer. So, these are popular as middle ranged computer. It is also multiple user computer and supports more than dozen of people at a time. It is costlier than microcomputer. It is also used in university, middle range business organizations to process complex data. It is also used in scientific research, instrumentation system, engineering analysis, and industrial process monitoring and control etc.

Mainframe Computer

Mainframe Computer is the large sized computer that covers about 1000 sq feet. It is general purpose computer that is designed to process large amount of data with very high speed. It accepts large amount of data from different terminals and multiple users and process them at same time. More than 100 users are allowed to work in this system. It is applicable for large organization with multi-users for example: large business organization, Department of examinations, Industries and defense to process data of complex nature. It uses several CPU for data processing. 
IBM S/390, IBM S/709, ICL 39, CDC 6600 are some example of mainframe computer.

Application Areas for Mainframe computer:

• Government and civilian
• Credit card processing
• Back Account management
• Marketing
• Business data processing in large organization
• Air traffic control system
• Industrial design

Characteristics of Mainframe Computers

 Some main characteristics of mainframe computers are:

• Run multiple programs concurrently
• Support many concurrent users
• Support new and legacy software
• Run many different kinds of operating systems
• Uninterrupted operation
• Have performance measured in millions of instructions per seconds (MIPS)
• Perform tasks on huge amounts of external data
• Are flexible even to run many kinds of applications and tackle broad business task.

Supercomputers

Supercomputers are the most powerful computers among digital computers. These consists of several processors running together thereby making them immensely faster and powerful. These computers are capable of handling huge amounts of calculations that are beyond human capabilities. Super computers can perform billions of instructions per second. Some of the today's supercomputers have the computing capability equal to that of 40000 microcomputers. CRAY X-MP-14,  CDC-205,ETA GF-10, FUJITSU VP-400, NEC SX-2, PARAM, PACE are some example of super computer. Supercomputers are mainly used in following purposes:

• Weather forecasting
• Nuclear science research
• Aerodynamic modelling
• Seismology
• Metrology

Characteristics of Supercomputers

Some main characteristics of supercomputers are given below:

• Focus processing power to execute a few programs or instruction as quickly as possible
• Focused on speed and accelerated performance
• Push boundaries of what hardware and software can accomplish
• Typically run a variant of Linux as their operating system
• Are typically run at maximum capability, putting the computer's full processing resources toward solving a particular problem
• Are often a cluster or grid of smaller computers working together on whatever problem they are looking to solve
• Have performance measured in floating point operations per seconds (FLOPS)
• Execute complicated computations using large internal memory
• Have dedicated purposes for tasks like scientific research or engineering models