1.1 Digital and Analog Computers

1.  A Digital Computer uses distinct values to represent the data internally.

• All information are represented using the digits 0's and 1's.
• The computers that we use at our homes and offices are digital computers.
• Digital signal represent particular state that is: 0 (low) or 1(high), yes or No, On or OFF, TRUE OR FALSE.
• These systems store and process the data in digital form (strings of 0's and 1's).
• They are capable of processing analog signals but the analog signals have to be converted into digital signals using an ADC before feeding into the digital computers.

2.  Analog Computer is another kind of computer that represents data as variable across a continuous range of values.

• The earliest computers were analog computers.
• Analog computers are used for measuring of parameters that vary continuously in real time, such as temperature, pressure and voltage.
•  Analog computers may be more flexible but generally less precise than digital computers.
•  Based on analog mechanism.
•  These are fast and multi-tasked.
•  Results displayed by these computers are less accurate.
•  Analog computers are used in hospital to measure the size of stone in kidney and mental disease diagnostics (CT scan with photos).
•  Powerful in solving differential equations.
•  These computers use OP-AMP (Operational Amplifier).
•  Examples: Seismograph

           1.1.1    Hybrid computer (digital + analog)

• These computers are a combination of both digital and analog computers.
• Hybrid computers are computers that exhibit features of analog computers and digital computers.
• The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as  a solver of differential equations.
• The hybrid computers can transfer data from analog to digital and digital to analog.
• Used in industrial process control, jet planes, airplanes.
• These computers are mainly used in hospital to measure the heart beat of patient.
• Simulation: Simulation is the process in which the computer system and program are used to produce.

Table 1.1 Types of Basic Computer

Computer	Input	Output	Based on	Examples
Digital	On/Off, 1/0	On/Off,1/0	Counting	General Purpose PC's
Analog	Measure Elements	Graph Pictures	Continuous Measurements	Weather Forecasting, Speedometer, ECG Machines etc.
Hybrid	Both 0/1 & Measure Elements	Both On/Off & Graphs	Counting & Measurements	Controlling & monitoring plants, Petrol pumpls, Modem, Simulation, Industrial process, Jet Plane etc.

Table 1.2 Comparison between Analog and Digital Computer

	Analog	Digital
Signal	Analog signal is a continuous signal which represents physical measurements.	Digital signals are discrete time signals generated by digital modulation.
Waves	Denoted by sine waves	Denoted by square waves
Representation	Uses continuous range of values to represent information	Uses discrete or discontinuous values to represent information
Example	Human voice in air, analog electronic devices.	Computers, CDs, DVDs, and other digital electronic devices
Technology	Analog technology records waveforms as they are.	Samples analog waveforms into a limited set of numbers and records them.
Data transmissions	Subjected to deterioration by noise during transmission and write/read cycle.	Can be noise immune without deterioration during transmission and write/read cycle
Response to Noise	More likely to get affected reducing accuracy	Less affected since noise response are analog in nature.
Flexibility	Analog hardware is not flexible	Digital hardware is flexible in implementation.
Uses	Can be used in analog devices only. Best suited for audio and video transmission.	Best suited for Computing and digital electronics.
Applications	Thermometer	PCs, PDAs
Bandwidth	Analog signal processing can be done in real time and consumes less bandwidth.	There is no guarantee that digital signal processing can do done is real time and consumes more bandwidth  to carry out the same information.
Memory	Stored in the form of wave signal	Stored in the form of binary bit
Power	Analog instrument draws large power.	Digital instrument draws only negligible power.
Cost	Low cost and portable.	Cost is high and not easily portable.
Impedance	Low	High order of 100 megaohm.
Errors	Analog instruments usually have a scale which is cramped at lower end and give considerable observational errors.	Digital instruments are free from observational errors like parallax and approximation errors.