Classification by their basic operating principle

Using this classification technique,
 computers can be divided into Analog, Digital and Hybrid systems. They are explained as follows:
  • ANALOG COMPUTERS
Analog computers were well known in the 1940s although they are now uncommon. In such machines, numbers to be used in some calculation were represented by physical quantities - such as electrical voltages. According to the Penguin Dictionary of Computers (1970), “an analog computer must be able to accept inputs which vary with respect to time and directly 7
apply these inputs to various devices within the computer which performs the computing operations of additions, subtraction, multiplication, division, integration and function generation….” The computing units of analog computers respond immediately to the changes which they detect in the input variables. Analog computers excel in solving differential equations and are faster than digital computers.
  • DIGITAL COMPUTERS
Most computers today are digital. They represent information discretely and use a binary (two-step) system that represents each piece of information as a series of zeroes and ones. The Pocket Webster School & Office Dictionary (1990) simply defines Digital computers as “a computer using numbers in calculating.” Digital computers manipulate most data more easily than analog computers. They are designed to process data in numerical form and their circuits perform directly the mathematical operations of addition, subtraction, multiplication, and division. Because digital information is discrete, it can be copied exactly but it is difficult to make exact copies of analog information.
  • HYBRID COMPUTERS
These are machines that can work as both analog and digital computers.