3 Computing System Fundamentals 3.5 Data Representation

3.5.5 Analogue and Digital

Binary data All data held & processed inside a computer are coded using binary machine code, i.e. can only be represented by two symbols, 0 and 1. The data are actually stored as electrical and magnetic states corresponding to these two symbols. Effectively, billions of microscopic switches are held in either on or off positions. However, it is easier for us to represent them with 1’s and 0’s.

Analogue Analogue information is information as it is encountered in "the real world", information such as paintings, photographs, symphonies, temperatures, atmospheric pressures, electrical current flowing in a wire, facial expressions, etc.

Analogue Analogue information is continuously varying (e.g. the temperature in a room changes constantly from second to second) and has no absolute value - the value we use is as accurate as the measuring instrument will allow. This type of information cannot be put directly into a digital system like a computer without conversion.

Digital Digital data on their own have no meaning until they are converted into a real-world context (you could say that this is what converts data into information): DATA + CONTEXT = INFORMATION.

A-D conversion Analogue information cannot be processed by a computer unless it is converted to a digital signal. Analogue signals are converted to digital values by an analogue-to-digital converter (ADC), usually by sampling the continuously varying information at regular intervals. The more frequently the data is sampled, the more accurate the digital representation.

D-A conversion The computer processes the data and then feeds back information to the user via a digital-to-analogue converter (DAC). These converters may often be together in an interface unit of some kind e.g. a modem is both an ADC and a DAC.