History Of The Computer Analog Or Digital

History Of the​ Computer; Analog Or Digital?
In 'History of​ the​ Computer - the​ emergence of​ Electronics',​ we​ saw how the​ development of​ Radar during the​ second world war led to​ an​ understanding of​ pulse technology .​
At the​ same time methods were refined for the​ calculations required for the​ ballistic trajectories .​
From these beginnings,​ the​ digital computer was developed.
What is​ meant by 'Analog' and 'Digital'? a​ couple of​ examples will explain the​ difference .​
An analog is​ something which is​ analogous,​ obviously,​ but you may know that an​ analogous process or​ function is​ one that is​ equivalent,​ or​ very similar to​ another one .​
An analogy is​ often used to​ explain,​ or​ to​ assist the​ understanding of,​ some new feature in​ terms that are understood.
For example a​ home electric circuit for house wiring to​ operate a​ lamp .​
The supply is​ controlled by a​ circuit breaker,​ when it​ is​ available at​ the​ outlet where the​ lamp is​ plugged .​
This can be compared to​ plumbing,​ where the​ water supply is​ controlled by a​ valve or​ tap on​ entering the​ home,​ then pipes carry the​ water to​ the​ kitchen,​ where the​ supply can be turned on​ or​ off by a​ tap or​ faucet,​ and is​ immediately available .​
The rate of​ flow of​ the​ water can be controlled,​ which is​ analogous to​ a​ dimmer on​ the​ lamp.
The analogy is​ not absolutely the​ same,​ but aids in​ the​ understanding of​ the​ electricity supply by someone who knows the​ plumbing system.
Digital,​ concerning digits or​ numbers,​ refers to​ the​ use of​ numbers to​ represent all things .​
As an​ example,​ a​ digital watch uses numbers to​ indicate the​ time .​
The numbers on​ the​ face of​ traditional watch are distributed around the​ dial,​ so that the​ hands pointing to​ them are analogous to​ the​ passage of​ time .​
For example the​ minute hand pointing straight down,​ half way through the​ circle of​ the​ clock,​ represents the​ passing of​ half an​ hour .​
If the​ hour hand is​ pointing to​ the​ number 3,​ this indicates 3 hours of​ the​ 12 for a​ complete circuit .​
When we​ learnt to​ tell the​ time we​ knew that this was half past three .​
The digital watch however says 3:30.
Closer to​ our topic,​ we​ can consider the​ evolution of​ the​ gramophone record .​
The vinyl LP was the​ standard medium for music recording and playing from the​ 1950s,​ tape recordings were also developed in​ parallel .​
Both these media use a​ modulation system,​ where the​ amplitude,​ or​ strength,​ of​ the​ modulation is​ proportional,​ or​ analogous,​ to​ the​ loudness of​ the​ original live singing or​ playing .​
This music had been converted by a​ microphone into a​ variable electrical signal,​ analogous to​ the​ sound.
With the​ invention in​ the​ 1980s of​ the​ Compact Disc,​ digital techniques were employed to​ represent the​ changes in​ sound levels,​ by using a​ sampling pulse to​ monitor the​ loudness of​ the​ sound .​
This sampling pulse is​ used at​ a​ high frequency,​ so that it​ is​ not audible,​ and traces the​ progress of​ the​ sound .​
The principle is​ analogous to​ the​ movie camera where a​ sequence of​ still pictures are shown at​ a​ rate of​ 32 frames per second,​ so that they appear to​ show a​ moving picture .​
Similarly a​ tv uses a​ frame rate of​ 50 or​ 60 per second (strictly speaking 25 0r 30 interlaced).
The big advantage of​ a​ digital recording and reproduction system (amplifiers etc are also digital) is​ that,​ due to​ the​ nature of​ the​ high frequency pulses,​ it​ is​ possible to​ copy them exactly when transferring from one medium to​ another,​ for example copying a​ from cd track to​ compilation cd .​
With an​ analogue system there are losses in​ every transfer,​ so that a​ recording on​ a​ cassette tape copied from a​ vinyl lp via a​ home stereo is​ noticeably poorer quality than the​ original.
A computer can also be analog or​ digital,​ though the​ digital type have vastly outgrown the​ analog .​
An analog computer might be used in​ research work,​ where,​ for instance a​ record may be made on​ a​ moving chart of​ the​ temperature and humidity in​ a​ room being air conditioned by a​ new design air conditioner,​ the​ chart could also be a​ display on​ screen .​
Either way,​ the​ graph is​ an​ analog representation of​ the​ temperature and pressure.
Early electronic controls in​ aircraft were run by a​ form of​ analog computer,​ the​ amount the​ ailerons moved was proportional to​ the​ movement of​ the​ joystick,​ but not directly proportional .​
a​ calculation was performed,​ which depended on​ the​ speed and height of​ the​ aircraft,​ and other factors .​
The electronic 'boxes' involved linear amplifiers and variable response circuits,​ all fed by sensors from the​ flight controls etc.
Subsequent articles in​ this series are concerned only with digital computers .​
We look at​ how they are put together,​ and how they perform,​ in​ simple steps,​ more and more advanced calculations.

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