i. Analog computer
ii. Digital computer
iii. Hybrid computer
i. Analog Computer: The analog computer measures continuous types of data and uses a physical quantity that changes along a constant scale.
Example:
Analog processor is used at petrol stations, which indicates the quantity of petrol delivered. A thermometer is an analog device because it measures the length of a mercury column which varies continuously. An analog clock measures time by means of the distance travelled by the hands of a clock around a dial.
A digital computer represents data in terms of discrete numbers and processes data using the standard arithmetic operation. It directly counts numbers (digits) that represents numerals, letters and other symbols. Digital computers use electronic circuits which can distinguish between just two values ‘0’ & ‘1’. All the data must be encoded digitally as 0’s and 1’s in the digital computers.
Example:
Earlier analog devices got their digital equivalents such as digital watches, digital scales and digital thermometers. Most of the computers available today are digital computers and therefore, term “computer” usually stands for “digital computer”.
iii. Hybrid Computer:
A hybrid computer combines the best features of analog and digital computers. It consists partly of the components of digital computer and partly of analog computer to combine the characteristics of both types (for example the speed of analog computer and the accuracy of digital computer). Therefore, hybrid computers help the user to process both continuous and discrete data. The results can be obtained either in analog signals or discrete signals that is either as continuous output in the form of graphs or as discrete digits.
Example:
Hybrid computers for example, control passenger flight radar. Other example of hybrid computers is the modern petrol pumps in which motor for pumping fuel runs in analogue fashion and the quantity of the fuel delivered or the cost of the fuel is represented in digits.