Digital refers to the property of dealing with the discrete values rather than a continuous spectrum of values: compare analog or analogue. The word comes from the same source as the word digit: the Latin word for finger (counting on the fingers) as these are used for discrete counting.

The distinction digital versus analogue can refer to data storage and transfer, the internal working of an instrument, and the kind of display.

The word "digital" is commonly used in computing.

Digital vs Analogue

Digital noise

When data is transmitted using analogue methods, a certain amount of noise enters into the signal. This can have a myriad of different causes: data transmitted via radio may get a poor reception, have interference from other radio sources, or pick up background radio noise from the rest of the universe. Electric pulses being sent down wires are impeded by the resistance of the wire, and heat variations can increase or reduce these resistances. Whilst digitally transmissions are also degregated, any slight variations can be safely ignored. Any variance could provide a great amount of distortion in an analogue signal. In a digital signal, these variances can be overcome, as any signal close to a particular value will be interpreted as that value.

Ease of reading

For human readable information, both digital and analogue display methods can be useful. Should an instant impression be required, analogue meters often give information quickly. Many people glance quickly at their watch and know roughly what the time is. A needle just touching onto the bottom of an orange shaded area is much different to a needle almost touching into the red area, but an indicator lamp would just glow orange. When accuracy is required, however, digital displays are preferred. Reading analogue meters requires time and a little bit of skill, whereas writing down the value on a digital display is merely a case of copying down the numbers. In cases where both accuracy and quick reckoning are both required, dual displays are often used.

Systematic loss of data

When an analogue source needs to be converted into a digital signal for processing by other digital systems, some data may be lost. The analogue to digital converter only has a certain resolution: whereas the human eye may be able to detect tens of thousands of different intensities of pure green, the CCD in a digital camera may only be capable of 256, and at a resolution of a megapixel or so. Whilst this information will be preserved in future transmission, the data has been lost.

It should be noted that photographic film is not perfect, and aberrations will appear in this. Losses in analog systems are often modelled as a noise spectrum and modulation transfer function (MTF). The MTF of many analog systems, including film, typically "rolls off" with increasing frequency.

Historical Digital Systems

Although digital signals are generally associated with the binary electronic digital system used in modern electronics and computing, digital systems are actually ancient, and need not be binary nor electronic.

Non binary, non electonic

Smoke signals are one of the oldest examples of a digital signal, where an analog "carrier" (smoke) is modulated with a blanket to generate a digital signal (puffs) that convey information.

Non binary, possibly electronic

Morse code uses five digital states - dot, dash, short gap (between each letter), medium gap (between words) and long gap (between sentences) - to send messages via a variety of potential carriers such as electricity or light. For example using an electrical telegraph or a flashing light.

Binary, audio

More recently invented, a modem modulates an analog "carrier" signal (such as sound), to encode binary electrical digital information, as a series of binary digital sound pulses. A slightly earlier, surprisingly reliable version of the same concept was to bundle a sequence of audio digital "signal" and "no signal" information (i.e. "sound" and "silence") on magnetic cassette tape for use with early home computers.

Binary, visual

A beacon is perhaps the simplest non-electronic digital signal, with just two states. It's either on fire, or not.

See Also