A computer can be classified as one of the following depending on the type of the data it is to process.
1. Digital Computers
2. Analog Computers
3. Hybrid Computers
In digital computers, mathematical expressions are finally represented as binary digital (0 and 1) and all operations are done using these digits at very high rate. The digital computer basically knows only how to add. Remaining operations like multiplication, division and exponentiation etc., are first converted into addition and the calculated. A digital computer operates in inputs that are on off or incrementally stepped quantities which are represented by numerical digits.
Analog is a Greek word, which means establishing similarities between two quantities. In analog computer, similarities are established in form of operated by measuring rather than by counting. For example, the speed of an automobile as measured by a speedometer, or the temperatures of a patient as measured by a thermometer.
Analog computers cannot compute directly with numbers. Rather, they deal with variables that are measured along a continuous scale and are recorded to some predetermined degree of accuracy. Temperature for example, may be measured to the nearest tenth of a degree of a Celsius scale. A petrol pump may contain an analog processor.
These computers will have the desirable features of digital and analog computers. For example, a patient monitoring system installed in a hospital will have to obtain the temperature of a patient analog and convert it to the nearest decimal value before displaying it in digital form.