History Of The Computer; The Emergence Of Electronics.

The history of the computer inevitably includes the development of electronics, we look at the explosive (!) growth of electronics in the late 1930s and early 1940s.

If anything could be said in favor of war, it may be that it speeds up the development of technology. Of course much of that technology is employed in killing people and destroying infrastructure, but there are also things which could be considered beneficial.

Electronics was around in the early part of the...

The history of the computer inevitably includes the development of electronics, we look at the explosive (!) growth of electronics in the late 1930s and early 1940s.

If anything could be said in favor of war, it may be that it speeds up the development of technology. Of course much of that technology is employed in killing people and destroying infrastructure, but there are also things which could be considered beneficial.

Electronics was around in the early part of the 20th Century, wireless, or radio, was in its infancy at the time of the first world war. Radio broadcasting came into prominence in the '20s and 30's, Television started in the '30's.

The second world war, from 1939 in Europe, and a couple of years later involving the USA, ended in 1945. Radar (Radio Aid To Detection And Ranging) was developed from early experiments, just prior to the war, in Britain and Germany. There was rapid development in the field, and, by the end of the war, Radar was being used in several fields.

Aircraft Navigation - Using ground transmitters in sets of 3, widely spaced, to give an aircraft using a receiver a method of pinpointing its position. This is a similar system to that used in gps today, substituting satellites for the ground stations.

Targeting - A beam was transmitted from a Radar station in England so that it intercepted a target in Germany. An aircraft could fly along the beam, guided by signals, dots or dashes, if it strayed off the beam, left or right. Known as flying on the beam.

Interception - a series of ground stations around the South-East coast of England, feeding into a central control room, where their tracks could be displayed, significantly assisted in the Battle of Britain (1940).

Airborne Interception (AI) - Developed towards the end of the war, used a Tranceiver (transmitter/receiver) in a night fighter to find a target in the dark, or bad weather, and track it to within firing range.

Beacon - A tranceiver was located at the end of a runway so that ground staff could guide a returning aircraft to land in bad weather, this became more and more sophisticated, developing into GCA or Ground Controlled Approach.

Shipping - radar equipped vessels could track other vessels in darkness or fog, whether peacefully or aggressively.

Many other sytems were developed or initiated in that 6 year period. Knowledge of electronics, and what it could be used for vastly increased. In parallel with the development of radar, other fields of electronics were also advancing, under pressure from the requirement to improve the technology.

Long range guns on ships or in the field needed to be aimed accurately. The calculations required in ballistics to aim a gun so that you can hit the target, or aim a V2 rocket so that it hits London from continental Europe, are phenomenal.

This, then was the scene at the end of the war. We knew how to tackle large calculations with speed, and we had developed a new concept in electronics, Pulse Technology. This is so called because radar uses short pulses of high energy, for two main reasons.

1. The pulses can be coded. For example, in the Navigation example we looked at, 3 ground stations transmit a signal whose source needs to be identified. One transmitter could transmit a series of single pulses spaced say 10 milliseconds. A second could transmit a pair of pulses at 10 millisecond spacing, and the third 3 pulses. A chart would tell the navigator where the pulse sets were transmitted from, and the distances obtained from the radar set used to locate the position on the chart.

2. The power, or strength, of the signal. A continuous radio signal, like a radio broadcast, takes a given amount of power. However, a 1 millisecond pulse every 10 milliseconds, uses only one tenth of the power, on average. So a radar transmitter can have a much greater range for the same power. This is is especially important in a primary (transmit and receive) radar system, where we must detect the reflection of the signal we transmit. Likewise a secondary (receive) radar system, for example the navigation system above, will have a bigger range.

Next we will look at how early computers were now possible due to these developments.

History Of The Computerflip-Flops - A Basic Counter

Flip-Flops - A basic counter

We looked at the Binary system, and basic computer logic elements, in previous articles, "It's a binary world - how computers count" and "How computers add - a logical approach".

Now we can combine two parts of these articles to look at a counter. Another common logic element in a computer is a counter or timer. This can b to count items going past a sensor on an assembly line, or possibly a count-down timer. For example, if you have a late ...
Flip-Flops - A basic counter

We looked at the Binary system, and basic computer logic elements, in previous articles, "It's a binary world - how computers count" and "How computers add - a logical approach".

Now we can combine two parts of these articles to look at a counter. Another common logic element in a computer is a counter or timer. This can b to count items going past a sensor on an assembly line, or possibly a count-down timer. For example, if you have a late model washing machine it will have a simple computer using a count down timer to give 10 minute wash cycle, etc.

There are several types of counter, nearly all of which use a basic element of electronics, the Flip-Flop. And you thought they were rubber shoes English people wear to the shower or the beach. (At this point Australians say "I thought they were called thongs").

OK back on topic. The flip-flop is as old as electronics, and is a classic example of the binary system. It has two possible stable states, A or B, and can be 'toggled' from one state to the other, just like a 'push-on, push-off' switch. It was originally made with two vacuum tubes (or one, for example a double triode).

It normally has two outputs, one being the complement of the other. That is,if one output(A) is a logic 0, the other(B) is a logic 1, and vice-versa. The input, or Toggle(T) is at logic 0 until a pulse from a sensor, for example, comes along. This pulse takes the logic state to 1, then back to 0. The toggle effect, causing the Flip-Flop to flip, is actually the CHANGE from 0 to 1.

 In logic terms the flip-flop is made up using AND and OR gates, in logic cicuitry it is just a 'black box' labelled FF. Several FFs may be grouped into yet another black box, a counter, timer, or multivibrator.

We can make up a Truth Table, which we have used before. If you recall, a truth table tells you what the Output will be for all possible Inputs.

TRUTH TABLE for Flip Flop - Toggle (C)hange,- Outputs A and B.

INITIAL STATE
T B A
0 1 0 'A' output is 0

PULSE #1
T B A
C 0 1 'A' output is 1

PULSE #2
T B A
C 1 0 'A' output is 0

Now we string some flip-flops together to make a counter. Say we have a sensor on a beer bottling machine, which has to count 5 bottles before switching the feed, we need to count up to 5, or 101 in Binary. We will need 3 flip-flops, for binary bits 0,1 and 2, corresponding to decimal bit value of 1,2 and 4.

We will take the A output of the 3 flip-flops to a decoder black box, which we can use to detect when we get to 5, then switch the feed. The B output of flip-flop 0 is passed to the toggle input of flip-flop 1 via an AND gate, so the next pulse from the sensor (which goes to all 3 flip-flops) at this AND gate will toggle the flip-flop, depending on the value of the B output, 0 or 1. Similarly the B output of flip-flop 1 goes to the toggle of flip-flop 3 via an AND gate.

Our 3 Flip-Flops now come up with a truth table like this:-

INITIAL STATE
FF2 FF1 FF0
TBA TBA TBA
010 010 010 'A' outputs 000 - 0

PULSE #1
FF2 FF1 FF0
TBA TBA TBA
C10 C10 C01 'A' outputs 001 - 1

[The (C)hange flips FF0 (always). FF1 & FF2 are blocked by the AND gate which needs a 0 input from the previous FF 'B' output AND the pulse change.]

PULSE #2
FF2 FF1 FF0
TBA TBA TBA
C10 C01 C10 'A' outputs 010 - 2

[The (C)hange flips FF0 (always). FF1 flips beacause the 'B' output from FF0 is a 0 when the Pulse arrives. FF2 is blocked as before.]

PULSE #3
FF2 FF1 FF0
TBA TBA TBA
C10 C01 C01 'A' outputs 011 - 3

[FF0 flips, FF1 is blocked again,as is FF2.]

PULSE #4
FF2 FF1 FF0
TBA TBA TBA
C01 C10 C10 'A' outputs 100 - 4

(FF0 flips, FF1 flips, FF2 flips.)

PULSE #5
FF2 FF1 FF0
TBA TBA TBA
C01 C10 C01 'A' outputs 101 - 5 count complete!

[FF0 flips, FF1 and FF2 are blocked.]

This counter can count up to 111, 7 decimal, it then resets to 0. A couple of interesting points to note are:-

1. FF0 flips every pulse. FF1 flips every 2 pulses. FF2 flips every 4 pulses etc. These facts can be used to make up a divider, which can be cascaded. For example the 4 pulse output can go to a second counter which also gives a 4 pulse output, totalling 16. This can be expanded to make up a decadic counter by decoding a count of 1010 (10 decimal) and using this to toggle the next counter, etc. What about 60 and 12 for your digital watch?

2. Look at the 'B' outputs from the counter. In sequence the values are:- 111, 110, 101, 100, 011, 010 (7,6,5,4,3,2 decimal). See the pattern? That's right - a countdown timer! We'll be using this in a later article.

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...

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.