A digital system is one that uses discrete values rather than a continuous spectrum of values: compare analog. 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 analog 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 analog
When data are transmitted using analog methods, a certain amount of noise enters into the signal. This can have a myriad of different causes: data transmitted by radio may be received badly, suffer interference from other radio sources, or pick up background radio noise from the rest of the universe. Electric pulses being sent down wires are attenuated by the resistance of the wire, and dispersed by its capacitance, and heat variations can increase or reduce these effects. Whilst digital transmissions are also degraded, any slight variations can be safely ignored. Any variance could provide a great amount of distortion in an analog signal. In a digital signal, these variances can be overcome, as any signal close to a particular value will be interpreted as that value.
Analog versus digital display; ease of reading
For human readable information, both digital and analog display methods can be useful. Should an instant impression be required, analog meters often give information quickly. Many people glance quickly at their analog watch and know roughly what the time is. When accuracy is required, however, digital displays are preferred. Reading analog 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.
A needle (analog) 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 (digital) would just glow orange.
Systematic loss of data
When an analog source needs to be converted into a digital signal for processing by other digital systems, some data may be lost. The analog 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 have been lost.
It should be noted that photographic film is not perfect, being subject to aberrations. 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 electronic
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.
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.
A beacon is perhaps the simplest non-electronic digital signal, with just two states. It's either illuminated, or not.
- Digital circuit
- Analog clock with digital display
- Digital Equipment Corporation
- Analog to digital converter
- Digital control
- Digital revolution