Analog and Digital

The word analog  denotes a phenomenon that is continuously variable, such as a sound wave. The word  digital, on the other hand, implies a discrete, exactly countable value that can be represented as a series of digits. Sound recording provides familiar examples of both approaches. Recording a phonograph record involves electromechanically transferring a physical signal  into an “analogous” physical representation. Recording a CD, on the other hand, involves sampling  the sound level at thousands of discrete instances and storing the results in a physical representation of a numeric format that can in turn be used to drive the playback device. Virtually all modern computers depend on the manipulation of discrete signals in one of two states denoted by the numbers 1 and 0.

Whether the 1 indicates the presence of an electrical charge, a voltage level, a magnetic state, a pulse of light, or some other phenomenon, at a given point there is either “something” (1) or “nothing” (0). This is the most natural way to represent a series of such states. Digital representation has several advantages over analog. Since computer circuits based on binary logic can be driven to perform calculations electronically at ever-increasing speeds, even problems where an analog computer better modeled nature can now be done more efficiently with digital machines. Data stored in digitized form is not subject to the gradual wear or distortion of the medium that plagues analog representations such as the phonograph record. Perhaps most important, because digital representations are at base simply numbers, an infinite variety of digital representations can be stored in files and manipulated, regardless of whether they started as pictures, music, or text

Converting between Analog and Digital Representations:-
Because digital devices  are the mechanism of choice for working with representations of text, graphics, and sound, a variety of devices are used to digitize analog inputs so the data can be stored  and manipulated. Conceptually, each digitizing device can be thought of as having three parts: a component that scans the input and generates an analog signal, a circuit that converts the analog signal from the input to a digital format, and a component that stores the resulting digital data for later use. For example, in the ubiquitous flatbed scanner a moving head reads varying light levels on the paper and converts them to Most natural phenomena such as light or sound intensity are analog values that vary continuously. To convert such  measurements to a digital representation, “snapshots” or sample readings must be taken at regular intervals. Sampling more frequently gives a more accurate representation of the original analog data, but at a cost in memory and processor resources. 12 analog and digital a varying level of current. This analog signal is in turn converted into a digital reading by an analog-todigital converter, which creates numeric information that represents discrete spots (pixels) representing either levels of gray or of particular colors. This information is then written to disk using the formats supported by the operating system and the software that will manipulate them.