Computers are classified in to various classes according to On the basis of working principle, On the basis of size, and on the basis of brand.On the basis of working principle computer are classified in to three types Ana log computer, Digital computer, and hybrid computer. Ana log computer measures continuous type of data and uses a physical quantity like electric current, voltage, temperature, etc. to present and process the data. It represent numbers by a physical quantity; that is, they assign numeric values by physically measuring some actual property, such as the length of an object, an angle created by two lines, or the amount of voltage passing through a point in an electric circuit. The computer which accepts discrete data as per the electric signals is known as digital computer. Basically , digital computers counts digits, which represent numbers or letters. The computers based on binary digits i.e. 0 and 1 are called digitals computer. It represents each and every information in terms of single numbers and processes the information by using standard arithmetic operations. Hybrid computer is the combination of the feature of Ana log and Digital computers.