Digital Electronics: Principles, Devices and Applications

608 Digital ElectronicsModemMemoryMouseCentralProcessingUnit(CPU)Input/OutputportsKeyboardRemovableStoragemedia (CDs,Floppy disks,etc.)AddressBusDataBusControlBusMonitorPrinterBasic ComputerPeripheralDevicesFigure 15.2Block diagram of a typical computer system.complexity of data processing to be done. Special-purpose computers, on the other hand, are designedfor a dedicated application. These computers perform a certain predecided and fixed sequence ofoperations. Typical applications include the computers used for weather forecasting, aircraft controlsystems, missile and other weapon guidance systems, etc.15.3.2 Classification of Computers on the Basis of the Technology UsedBased on the technology used, the computers are classified as analogue computers, digital computersand hybrid computers. In analogue computers, the input data comprise continuously changing electricalor nonelectrical (temperature, pressure, speed, volume, etc.) information. There are numerous examplesof analogue computational devices. One such device is the speedometer of an automobile. The inputdata to this device or machine are the continuously varying rotational speed of its driveshaft. Therotational motion is converted into a linear movement of a needle pointer that indicates the speedin km/h. A tachometer used to measure the rotational speed is another device of the same type.The input data in the case of a digital computer are discrete in nature. They are represented by abinary notation in the form of 0s and 1s. A hybrid computer is a mixture of the two. It attempts tocombine the good points of both analogue and digital computers. In a typical hybrid computer, themeasuring functions are performed the analogue way while the control and logic functions are digital innature.