It was Thirty Years Ago Today

Unusual view of Downtown San Francisco, from the Legion of Honor

Unusual view of Downtown San Francisco, from the Legion of Honor

It was almost exactly thirty years ago today—on Friday 9th October, 1987—that I first set foot in California.

On that occasion, I had come to the US only as a temporary visitor, to attend a job interview. It was a truly “temporary” visit, lasting only 4 days.

Until then, I had been anything but an experienced international traveler. I’d never been to any part of the USA before, and in fact I’d only been out of Britain three times during my life (and one of those trips was to Guernsey).

Broadening My Horizons

Ever since my undergraduate days, the idea of “working abroad” had been floating in the background as a vague possibility.

In 1986, I even went to Munich for a day, for a job interview with Siemens, but, even though they seemed keen to hire me, I did not pursue that possibility further.

Certainly, the idea that I might one day find myself living and working within sight of the Pacific Ocean never entered my head. It wasn’t until after I’d already moved here that I remembered that we had spent an entire term studying the state as part of our high school Geography course! I had basically ignored the course because it seemed to have no possible relevance to my life.

The Lure of the Dollar

As an Imperial College undergraduate, I began to hear stories of graduates who were obtaining what seemed like spectacular jobs in the USA, straight out of college. The starting salaries for these US jobs were apparently many times those that were offered to even the best British graduates. The figures seemed even more impressive because the dollar and pound were close to parity at that time. Nonetheless, the jobs I was told about were all on the US East Coast; in New York or Maryland.

My goal in getting an EE degree had been specifically to obtain a job with the BBC, which I did on graduating, so initially I felt that the die was cast and I’d already achieved my ambition.

However, my subsequent experience with the BBC and other British engineering employers was a huge disappointment. It seemed that not only were graduate salaries low, but conditions were poor and employers were either inefficient or unstable. I began to think once again of those tantalizing tales I’d been told about the wonderful jobs that were supposedly available in other countries!

The Window Opens

In 1987, I was working as a video systems hardware design engineer for a small company in Berkshire. One of my employer’s competitors was an American company, but had a European operation based in Reading. Word got around that I was looking for new employment, and the competitor contacted me to ask whether I’d be interested in working for them in Reading.

I declined to consider working for them in Reading, at which point they asked whether I might instead be interested in a job in California. Ah, now it’s getting interesting

Following several international phone calls, I managed to arrange an interview appointment at the company’s offices in Northern California. I had to obtain a B-1/B-2 visitor visa just to enter the USA, which meant that I also had to make a trip to the US Embassy in London before departing the UK.

San Francisco or Suffolk?

The plan was that I would arrive in San Francisco on a Friday evening, then have the weekend to do some sightseeing and recover from jet lag. My formal interview would be on Monday, then on Tuesday I’d fly back to Heathrow.

I would obviously have to take some vacation time from my job, but I felt that my current employer would not believe that I was going to California for a holiday just for the weekend! Therefore, I decided to tell them that I was going to visit the US air base at RAF Lakenheath, Suffolk. My mother had an American friend who was a teacher on the air base, and I’d visited her there previously, so it wouldn’t seem out-of-the-ordinary.

It was important to bear in mind that there was no guarantee that the company in California would actually offer me a job. I needed a plausible cover for my actions, so as not to jeopardize my existing position.

Offered the Job

To cut a long story short, I was offered the job in California within a few weeks following my interview. Somewhat to my surprise, my new employer was eager for me to start work there before Christmas, so I began the process of arranging to move myself and all my worldly possessions some 5500 miles.

Nonetheless, I would only be working in the US on a temporary, three-year E-2 visa, so there was always the possibility that I would choose to return to Britain (or might have to do so when the visa expired).

Way Out West. The Pacific Ocean from Pillar Point

Way Out West. Sunset over the Pacific Ocean from near Pillar Point

Return to a Hurricane!

I arrived back in the UK on Tuesday, 13th October, and went back to work the following morning as though nothing unusual had happened. Later that same week, however, the Great Storm of 1987 occurred.

On the night of October 15th, I didn’t hear the weather forecast, so the first I knew of the severity of the storm was when I set off on my 40-mile commute from Andover the following morning, and began noticing that tree branches were down everywhere, even blocking some roads.

[Update: On 15th October, the London Evening Standard published this article about the storm.]

Devastation in Brighton

In those days I was the Treasurer of the Southern Centre of the Royal Television Society, and, prior to my jaunt to California, I had volunteered to help out at the Society’s booth at that year’s International Broadcasting Convention (IBC), which was always held in Brighton. I traveled to Brighton the week after the storm, to see that many of the city’s trees had fallen, and a massive cleanup operation was underway.

It made me think that perhaps the country I’d been born in was itself becoming unrecognizable, so my life was going to change anyway, whether or not I emigrated.

Autumn Then & Now

 

Autumn in Hackness, Yorkshire, 1966

Autumn in Hackness, Yorkshire, 1966

My father took the color transparency above, in Hackness, Yorkshire, during one Autumn in the mid-1960s. It’s a good example of an annual event that we always looked forward to: the “Turning of the Leaves” on deciduous trees. In the photograph, you can see my mother and my brother strolling through “Autumn’s golden gown” on the right.

Growing up in England, the onset of each Autumn brought a variety of both welcome and unwelcome events.

The school year always started in September, and, given that I always hated school, that was definitely not a joyous event. On the other hand, when I was at Primary School, our teachers would often organize some kind of Harvest Festival celebration, which I did enjoy. Given that the North Riding of Yorkshire had a heavily agriculture-dependent economy, harvest time was far from being just a symbolic event.

While out in the countryside admiring the foliage colors, we also quite often stopped to pick wild blackberries (brambles) from roadside hedges, where berries were in abundant free supply. It was also sometimes possible to find and pick bilberries in similar locations. I participated in that, but I must admit that I enjoyed the results much more than the actual task! The traffic levels on country roads in those days were generally light, so it was usually no problem to pull the car over to the side of the road wherever we spotted some fruit, as shown below, where my father had parked our Humber Super Snipe to let my mother sample some likely-looking brambles.

Picking Blackberries in Hackness, 1966

Picking Blackberries in Hackness, 1966

Other autumnal events that I welcomed with glee included Guy Fawkes Night (aka Bonfire Night) each 5th November. At that time, Guy Fawkes was the only regular event in Britain at which fireworks were let off (the tradition of fireworks at New Year didn’t start until much later). Fireworks were sold to the general public because, given the damp climate and the time of year, there was little fire danger.

I also looked forward to the arrival of the Winter Catalogues. In those days there were few large stores in or near Scarborough, so my mother did much of her shopping via mail-order “catalogues”, such as Kays, Grattans or John Moores. There were two editions of each catalogue each year: for Summer and Winter. I eagerly anticipated the arrival of the Winter editions in September or October, because those editions included larger selections of toys, and I had Christmas and a birthday coming up for which to make my choices (or at least to dream about them!).

Excerpt from Grattan Catalogue, 1966

Excerpt from Grattan Catalogue, 1966

The image above is part of a page from the Winter 1966-67 Grattan catalogue. The pre-decimal prices shown are explained in my previous post: Old Money.

Fall in California Wine Country

The seasons in California are less pronounced than in England, but we do have noticeable autumnal changes.

A Laughlin Road Vineyard, Sonoma County

A Laughlin Road Vineyard, Sonoma County

I took the photograph above last weekend of a vineyard at Laughlin Road, Santa Rosa, just near Sonoma County Airport.

Unlike similar species in Britain, California native oaks are “live”, meaning that they do not shed their leaves during the winter (as shown in the photo). Nonetheless, the leaves of the (non-native) vines do change color, and you can just see that process beginning in the photo above.

Once the leaves have changed color, they tend to stay on the trees longer in California than in Britain (probably because California is less windy). The photograph below was taken in Moraga a few years ago, in mid-December. (The photograph is marred only by the bus stop sign in the foreground!)

Autumn Leaves in Moraga

Autumn Leaves in Moraga

I plan to write further posts about Autumn in California, as the season progresses.

You Can Call Me Al(phonse)

H G Wells Society Lecture on Hypnosis, 1982

H G Wells Society Lecture on Hypnosis, 1982

The image above is somewhat adapted from an ink-and-brush poster that I designed for a 1982 lecture on Hypnosis, presented by Imperial College’s H G Wells Society.

Like many artists, I have drawn much inspiration from the work of others. Some have said that no art exists in a cultural vacuum; all art is in some way derived from that of previous works. For this poster, I was strongly inspired by a poster created by the great Czech Art Nouveau illustrator, Alphonse Mucha.

At that time, while trying to generate ideas for the design of the Hypnosis lecture poster, I’d just bought the book Alphonse Mucha: the Graphic Works (cover shown below) from the nearby Victoria & Albert Museum.

Mucha Graphic Works Book Cover

Mucha Graphic Works Book Cover

One work that was reproduced in the book, and which particularly appealed to me, was a poster produced by Mucha for a 1921 exhibition of his own work at the Brooklyn Museum in New York.

I borrowed ideas not only from Mucha, but also from other artists; in fact, the line technique that I used for the hair was inspired by the work of the British illustrator, Robin Jacques.

The Poster

Frankly, my poster design was a bit of a muddle (to put it mildly), because, although it was a striking design that achieved its purpose of attracting attendees to the lecture, I’d completely lost sight of the Art Nouveau style of Mucha’s composition.

For that reason, I decided that I didn’t want to reproduce the original poster here, so the illustration above is an adaptation of my original painting, with some of the most incongruous aspects covered over or redrawn!

My design is monochrome-only, for reasons that I explained in a recent post on my professional blog. The Student Union’s printing equipment was not capable of printing in full color, so, for speed and simplicity, all my poster designs were monochrome.

The Lecture

The lecture on hypnosis that my poster advertised was presented by Martin S Taylor, who soon thereafter went on to become the Editor of the Imperial College Student newspaper, Felix (which traces its ancestry back to the founding of the Science Schools Journal by H G Wells).

I recall Martin’s lecture (and accompanying demonstration) as being utterly fascinating, as indeed were most of the H G Wells Society’s presentations at that time.

Martin’s successor as Felix editor was Pallab Ghosh, whom I’ve already mentioned in a previous post.

Martin was an IC student at the time of the lecture, but apparently he went on to make something of a career of hypnosis, as described on his own web site: http://www.hypnotism.co.uk/

Old Money & LSD

British Ten Shilling Note

British Ten Shilling Note

If you’ve concluded from the title of this post that I’m going to discuss illegal psychedelic drugs, then you may be in for a disappointment! What I’m actually going to discuss is the old British currency system, which has now vanished, but was still in use for much of my childhood.

The image above shows the front of the old “ten shilling note”. Until I scanned this image, I hadn’t handled one of these notes since they were withdrawn in 1969!

As a result of the arcane symbols used for its 3 denominations (explained below), the pre-decimal British currency came to be known as the LSD System.

In a previous post on my professional blog, I discussed some of the illogical and inconsistent spelling conventions of the English language. The old British currency system seemed equally illogical and arcane! Some have even suggested that whoever concocted the LSD System must have done so after taking a significant dose of some psychedelic drug!

By the time that I was born, in 1960, this system had been in use for many hundreds of years, so that acquiring fluency in it was accepted as a necessary and natural part of our education.

The LSD System

Under the LSD System, the primary unit of currency was the pound, but one pound was subdivided into twenty shillings, and each shilling was further divided into twelve pence.

1 Pound = 20 Shillings

1 Shilling = 12 Pence (Pennies)

There was a half-penny coin (called a ha’penny, and pronounced hayp-ny), and a quarter-penny coin (called a farthing) had been withdrawn only in 1960.

You could be forgiven for thinking that, in view of the actual names of the 3 currency denominations, the currency system would have been known as the “PSP System”, but that would have been far too obvious! Instead, obscure non-English terms were used, as follows.

LSD = Livra, Solidus, Denarius

Livra

The symbol used for the pound was “£”, which (my father assured me) was in fact an upper-case letter “L” with a cross through it!

One might have been forgiven for expecting that the symbol for pound would be some variation on the letter “P”, but that would have been too obvious. Why use pedestrian English, when there are so many other languages from which words may be borrowed? In this case, the “L” was derived from the Latin word livra, meaning “pound”.

Solidus

The symbol used for “shilling” was the refreshingly straightforward “s”, although it would be naïve to jump to the conclusion that the symbol was merely the initial letter of that word.

On the contrary, the “s” was the first letter of the Latin word solidus, which had been a Roman coin denomination, worth 1/72nd of one pound of gold.

Denarius

The symbol used for penny, or pence, was “d”. Why so?

If you think back approximately two thousand years, to the period when what is now England was a province of the Roman Empire, you may just recall that the Romans minted a silver coin that they called a denarius. Following the collapse of the Roman Empire in the West, the kingdoms that sprang up to fill the power vacuum continued to mint denarii of their own.

Around the year 755, King Offa of Mercia (a kingdom that later became part of England) introduced a new silver coin, the penny, as an equivalent to the Frankish denier.

British pennies ceased to be minted from silver after 1795, but the “d” symbol stuck.

LSD Arithmetic

The arithmetic of the LSD system involved carrying twelves from the pennies to the shillings column, and carrying twenties from the shillings to the pounds column.

As students, we accepted the difficulties associated with working with bases of twelve and twenty, if only because we had already been taught time computations, which did, and still do, involve base-sixty and modulo twelve calculations.

The Cryptic Codes

Having learned the cryptic symbols used to identify the currency denominations, we might have expected that an amount such as, for example, one pound nine shillings and six pence would be written as ‘£1 9s 6d.’

Such a representation was acceptable, but there were also many other possible configurations. The same amount could also be written as £1-9-6 or £1/9/6.

In certain price lists, to save space, there was no ‘pounds’ column, so the same amount would be written 29/6. See the Dinky Toys catalog example below.

For amounts less than one pound (such as the prices of groceries), it was usual to write, for example, one shilling and nine pence as 1/9, read as “one and nine”.

In cases where the price was an exact number of shillings, a further quirk was deployed. Instead of writing, for example, 3/0, the accepted formulation was 3/-.

Needless to say, it took me as a child some considerable time to master these peculiar shorthand forms.

Dinky Toys 1966 Price List

Dinky Toys 1966 Price List

The image above shows part of the price list from the 1966 Dinky Toys catalog. The conventions used for displaying prices in shillings and pence can be seen on the right. Note that for items costing more than £1, the price is still shown in shillings and pence only. For example, the “Holiday Gift Set” costs “37/6”, which is actually £1/17/6.

Strange Names

The colloquial name for a pound was a quid, and you can still use that term for the modern pound today.

Most British coins had acquired names (either officially, or as slang) in addition to their values. I’ve already mentioned the ha’penny and farthing (whose name was derived from “fourthing”), but there were many other colorful epithets.

Tanners, Bobs & Florins

The slang term for the sixpence coin was a tanner; that for a one shilling coin was a bob; while the two shilling coin was officially named the florin (because it had originally displayed a floral design). In fact, the florin was a rather late introduction, having been created during Queen Victoria’s reign (in 1849), ostensibly as a first step towards decimalization (the florin being worth one tenth of a pound). If indeed it was the first step towards decimalization, then it was also the last during Victoria’s reign!

The Last British Florin Design

The Last British Florin Design

Thruppenny Bit

There was also a three pence coin, which was colloquially referred to by the relatively obvious name of thruppenny bit. The inconveniently small silver thruppenny bit was withdrawn in 1942, and replaced by a twelve-sided nickel-brass coin.

This enforced a change in Christmas tradition. It had been the practice to cook a silver thruppence in each Christmas pudding, the lucky finder of which kept this small treasure trove. However, the new nickel-brass coin reacted with the pudding’s ingredients, to produce an unpleasant taste. Therefore, inflation took its effect, such that it was now necessary to cook a silver sixpence in Christmas puddings!

Half-Crown

Moving on up the value scale, the half crown coin was worth two shillings and six pence. There had, in earlier days, been a crown coin, worth five shillings, but, by the time that I came into the world, the crown was no longer in general circulation, and was minted only for special occasions. (The occasion of Sir Winston Churchill’s funeral, in 1965, was the first time that I saw one.)

Sovereign

During my lifetime, there was no pre-decimal coin in circulation having a higher value than the half crown. The denominations of bank notes were ten shillings, one pound, five pounds, and so on upwards.

When first introduced (in 1489), the pound had been a gold coin, called a sovereign (because its design depicted the King—in the person of Henry VII—at the time). Gold sovereigns are still minted today, but, if anyone should offer to sell you one of these for a pound, don’t expect it to be real!

Guinea

As if all the above were not sufficiently complex, the British managed to add a further layer of intricacy by adding elements of the class system to the currency system!

Minted alongside the pound, there had, for centuries, been a gold coin called a guinea (primarily because the coins had originally been minted, in 1663, using gold obtained from “Guinea” by the West Africa Company). Because of its intrinsic value, the equivalent in shillings of a guinea varied over the years, from twenty shillings when first introduced, up to thirty shillings in the 1690s, and then finally settling at twenty-one shillings.

By the twentieth century, however, the guinea coin had been long withdrawn, and the guinea was not an official currency denomination. Nonetheless, an attitude had developed among the upper classes that dealing in mere pounds was the grubby necessity of those who must work for a living. The leisured classes should never be seen to debase themselves with such proletarian considerations! Therefore, those who considered themselves as belonging to the “professional” class, or higher, always dealt in guineas (one guinea being worth twenty-one shillings), rather than in pounds.

A satirical example of this practice appears in Lewis Carroll’s tale: Through the Looking Glass. One character in the story, the Mad Hatter, always wears a top hat, in the brim of which is affixed a label stating; “In this style: 10/6”. The ‘10/6’ is the price—ten shillings and sixpence, or half a guinea, indicating—via the additional sixpence—that the hat is intended for a “professional” clientele.

The class distinction implied by the use of the guinea was satirized for perhaps the last time in the 1960s television show The Avengers.

In the episode entitled The Morning After, the hero, Steed, has captured a double agent called Jimmy Merlin. As they walk along, handcuffed together, Merlin decides to try to buy Steed off.

Merlin: “Any chance of making a deal?”

Steed: “I shouldn’t have thought so, but keep talking.”

Merlin: “Twenty thousand, in a Swiss bank account? No names; no strings?”

Steed: “Pounds?”

Merlin: “Yes.”

Steed: “Very sorry, old chap, only deal in guineas.”

Winds of Change

That was the way things were, and they had been that way for centuries. But no sooner had I learned the arithmetic of the LSD system, when, during the mid-1960s, someone announced: “You know that money system that we’ve been using for hundreds of years? Well, we’re not going to do that any more!”

Between 1968 and 1971, adjustments were made to the existing coinage, to bring it more closely into alignment with the planned decimal system.

In 1968, the minting of shilling and florin coins was terminated, and instead were minted, respectively, five new pence and ten new pence coins. The replacement coins were of the same size, shape and weight as their predecessors, but displayed the new values. During the next few years, various withdrawals occurred of denominations that would not convert conveniently to decimal values.

D-Day

Then came “D-Day” (the “D” standing, in this case, for “decimalization”). On February 15, 1971, the entire nation changed over from the official usage of one currency to the other, literally overnight.

On ‘D-Day’, all the surviving old coin denominations were called in, and the half new pence, new penny, and two new pence coins were issued for the first time. This vast changeover was achieved efficiently, by the expedient of placing the burden of the conversion upon sellers!

Sellers were to display their prices in the decimal currency as from D-Day, and, when purchasers wished to pay using the old currency, the seller would have to convert the amount for them. The seller accepted the old currency equivalent, paid back any change in the new currency, and then turned in the old coinage to their bank in the normal course of events.

The Chaos Caused by New P

In the decimal system, the pound was retained, with the same nominal value as the LSD pound.

There were to be one hundred new pence to one pound, with no denomination equivalent to the shilling. This implied that one new penny would be equivalent to 2.4 old pennies. The symbol for the decimal pound was retained as “£” (the crossed “L”), since this would cause no confusion, but the symbol for the new penny was to be “p”. This led to the practice of referring to, say, ten new pence as “ten pee”, to avoid the ambiguity that would arise from the use of the phrase “ten pence”.

Nonetheless, the requirement to specify ‘new pence’ played havoc with the colloquial terminology that had been commonplace until then.

The half new penny coin, for example, was never referred to as a “new ha’penny”, but initially as a “half new pence,” and later, when the word ‘new’ was dropped, a “halfpence.”

The nation’s Boy Scouts, who had traditionally undertaken their annual “Bob a Job” week, whereby they offered to perform chores for payment of one shilling, now found themselves forced to offer the less linguistically satisfying “Five New Pence a Job” week.

Goodbye to Ten Bob

As I mentioned above, the ‘ten bob note’ was withdrawn, and replaced with the seven-sided fifty new pence coin, in 1969.

Other than that, however, no changes were made to the paper money denominations as part of the decimalization plan.

Sing a Song of Two Sixpences Only, Please

I have not mentioned the withdrawal of the pre-decimal sixpence coin, because, in fact, this survived in use for some years following decimalization, but under the extremely quaint constraint that these coins be used only in pairs!

It was acceptable to pay an amount of five new pence using two sixpence coins, but it was illegal to use one sixpence coin to pay two and a half new pence!

Fading Memories

For those Britons who did not live through the decimalization era, the details of the LSD system described above fall very firmly into the category of rapidly receding ‘ancient history’.

That fact was brought home to me when my nephew, on seeing a reproduction of a 1930s travel advertisement stating, “Return Fare: 1/9,” asked me, “What does it mean: ‘Return Fare: one-ninth’?”

Complexity from Simplicity

Commodore776M

Commodore 776M Calculator: Our Family’s First Computer!

This flashback is slightly unusual, in that, instead of discussing an old photograph, I’m thinking about something that, back in the 1970s, seemed to me to be a technological miracle. Learning how it worked, and how to design even more complex devices, provided a valuable lesson in how amazingly complex systems can be built from simple components. The image above is my drawing of the first “digital computer” that my family ever owned: a Commodore 776M calculator.

This article explains how, in the space of less than 10 years, I went from regarding computers as mysterious marvels, to learning not only how they work, but also how to design and build them. I even obtained patents for my own new digital circuitry inventions. I’ve tried to keep the technical discussion as basic as possible, while still trying to show how complex systems are built up from simple components.

As I mentioned in a previous post, when I was at school I studied Advanced-Level Math and Physics, but much of what we were taught, even in Physics, was very theoretical, and it wasn’t at all clear how the principles applied to real-world technology, or indeed how real devices worked. To learn how real systems worked, I often had to resort to teaching myself.

Computers as Black Boxes

The same was true for understanding how computers worked. I was very excited when I was told that, as part of the Physics syllabus, we were going to learn to understand computers, but I was quite disappointed by what we were actually taught.

The teacher explained to us that digital computers use binary arithmetic (the value of every digit can only be 0 or 1), and that computers are built from simple circuits such as so-called “AND” and “OR” gates. The binary 0 and 1 values are represented in the computer by “low” and “high” voltages respectively.

We were able to play around with pluggable electronic “black box” modules that implemented these functions, and we confirmed the results of combining them. We could use Boolean Logic to combine the outputs from these gates.

But I still thought, “How do you get from that to a digital calculator?”

The answer (as I was to learn later on) is by combining thousands or millions of those basic gates together to make devices of increasing complexity.

Even after a career of designing digital electronic systems and the software associated with them, I still find it really astonishing how extremely complex devices can be created from such simple basic blocks.

Building Everything from NAND Gates

There are three basic types of digital computer logic circuit or “gate”:

  1. NOT gate. The output level is the opposite of the single input level.
  2. OR gate. The output level is high if any of the input levels is high. A NOR gate is the same but with the output inverted (i.e., an OR gate plus a NOT gate).
  3. AND gate. The output level is high only if all the input levels are high. A NAND gate is the same but with the output inverted (i.e., an AND gate plus a NOT gate).

It turns out that all three basic types of digital computer circuit can be built by combining one basic type of circuit, the NAND Gate.

A Real NAND Gate

My Advanced-Level Physics studies did not include electronic circuit design, of course, so it would have been unreasonable to expect to be taught exactly how these gates were implemented. I learned the details later on while studying for my Electronics degree.

The actual circuit for a real NAND Gate, implemented as Transistor-Transistor Logic (TTL) is as shown below. This is the diagram for one quarter of the Texas Instruments 7400 NAND Gate (because the actual chip contained 4 such circuits).

Circuit Diagram of Texas Instruments 7400 NAND Gate

Circuit Diagram of Texas Instruments 7400 NAND Gate

At the time that I began designing hardware, during the 1980s, TTL logic such as this was still the standard way of implementing many designs. I used these gates myself for many designs, starting with my undergraduate final-year project at Imperial College.

To avoid all the circuit details, the entire NAND gate can be represented with a symbol, as below.

NANDGateSymbol

NAND Gate in Symbolic Form

The diagram below shows how the connections on the symbol correspond to those in the actual circuit.

7400TTLCircuit2

TI 7400 NAND Gate: Symbol & Circuit

Memory from NAND Gates

To create a useful computer, you need to be able to store numbers in some type of memory.

It turns out that, by combining together a few NAND gates, you can create a simple memory for one bit of information. The combination is called a bistable circuit (aka a flip-flop), because (while the power is on) it remains in one of two stable states until an input causes it to change state. This allows you to store the outputs from logic circuits. Each bistable circuit allows you to store 1 bit of binary data.

Here is a diagram of a bistable 1-bit memory circuit, constructed entirely from NAND gates.

DataFlipFlopNANDs1

Data Flip-Flop (1-bit Memory) built from NAND Gates

The “Clock” input in this circuit can be obtained from another simple circuit constructed from NAND gates; the astable circuit, whose output continually oscillates between low and high states.

By lining up 8 bistables in parallel, you can store one byte of data.

From Gates to Functions

Well, that seemed simple enough, but I still didn’t understand how to get from that to a digital calculator.

Building a set of flip-flops gives you a way to store a number, but how do you combine numbers together? After all, the device is called a “computer” so how does it actually “compute”?

Well it turns out that you can also construct arithmetic circuits from—you’ve guessed it!—NAND gates. For example, you can build an adding circuit (called a Full Adder) to add together two 1-bit numbers, as shown below.

1-Bit Full Adder Circuit built from NAND Gates

1-Bit Full Adder Circuit built from NAND Gates

The circuit adds two 1-bit numbers, A and B, and accepts a carry-in bit from another adder (Cin). It generates the sum of the bits and the Cin  at S, and also a carry-out at Cout. By arranging any number of these adding circuits in parallel, and connecting their Cin inputs and Cout outputs to each other, you can build an adding circuit for numbers of any size.

Displaying Numbers

When you’ve constructed all the circuitry to allow users to type in numbers and compute the results, you still need a way to display the result to the user, because your calculator will be fairly useless without that.

Those early calculators used “seven segment” displays, which are sets of light-emitting diodes arranged so that, by switching segments on and off, any digit between 0 and 9 can be displayed in a human-readable form.

SevenSegmentDisplay

Seven-Segment Digital Display

So, how do you make the segments light up to display a particular number? Well, as you may have guessed by now, the answer is another logic circuit, called a Seven-Segment Display Driver. Texas Instruments also produced an integrated circuit to provide this function; the 7447 IC.

Complexity in Biology

Learning how complex computers (such as the device on which you’re reading this article) can be built from large numbers of very simple components made it easier for me to understand how the same principle could apply in other fields.

For example, in biology, evolution has created incredibly complex organisms (such as humans) from huge numbers of very basic cellular components. It’s much easier to understand such processes when you know how other complex systems are created, even though the results remain astonishing in all cases.

Ganton Railway Station: Flashback 40 Years

GantonSignalBox770823cright

Ganton Signal Box and Railway Crossing, North Yorkshire, August 1977

I mentioned in a previous post that during 1977-78, as part of the research for my A-level Art study, I surveyed local road and rail architecture. One site that I visited was that of Ganton Railway Station, on the line from Scarborough to York.

The photo above was taken on 23rd August 1977 (almost exactly 40 years ago), which was obviously a beautiful day. Ganton signal box basks in the sunlit calm, awaiting the next train, with the signalman’s Mini car parked alongside. The signal box was a standard North Eastern Railway Southern Division design of about 1870, but an interesting and unusual feature of it was the large oriel window on the left side. The extra window was provided so that the signalman could have a view up and down the road before closing the crossing gates.

The road that crosses the railway here never saw much traffic, because it leads only to Ganton Golf Course and a few farms. Nonetheless, the crossing was fully guarded and the signal box, which also controlled a block section of the railway line, was manned during operational hours.

Ganton Station had already closed long before my visit, and even at that date the station building itself had been demolished and replaced by a private house (the garden of which is visible on the right in the photo above). The station actually closed to passengers very long ago, in October 1930, along with all the other intermediate stations on the same line.

It was all part of a forward-thinking experiment by the LNER, to streamline operations on the York-Scarborough line by closing all intermediate stations and replacing the stopping services with buses. Much later, during the 1950s and 1960s, such closures and bus replacements became common, but it was quite a new concept in 1930.

All the stations remained open for freight (and occasional excursion trains) until the mid-1960s, when they finally closed completely, and the platforms were demolished.

Even though the railway line remains open, much of the railway architecture along its length has been demolished over the intervening years, leaving an empty and derelict landscape.

GantonSignalBoxSite2007

Site of Ganton Signal Box, 2007

I returned to the site of Ganton Station one dull afternoon in 2007, while back in Scarborough temporarily, seeing my family there. As shown above, what is left is ugly and depressing. The hedges around the private house (on the right) have grown up, but the signal box and all other railway buildings are gone. The crossing is now fully automatic, and there is very little evidence that there was ever a station at the site.

The lack of human presence at the site may be welcomed by the local wildlife, however. During my 2007 visit, a couple of wild rabbits were exploring in abandoned rails in the former coal yard by the side of the track, as shown below.

GantonSignalBoxRabbits2007

Rabbits at the site of Ganton Coal Yard, 2007

Living by the Sea

 

Ice Cream on Scarborough Beach, September 1963

Ice Cream on Scarborough Beach, September 1963

The photo above shows (from left to right) my mother, me and my brother enjoying ice cream cones on the beach in September 1963.

I generally don’t give much thought to the fact that I’ve spent most of my life living in coastal areas, in homes which, even if some did not have a direct view of the sea, were only a few miles from it.

This wasn’t entirely a deliberate policy on my part, and things just seem to have worked out that way. Nonetheless, I’m very glad that things did work out that way!

As I’ve mentioned in previous posts, my parents and my grandparents all came from Leeds, and they used to look forward to annual vacations in Scarborough and other coastal Yorkshire towns. (They usually seemed to choose Yorkshire destinations, although my grandparents did occasionally venture further afield, to such exotic locations as Grange-over-Sands!)

In those days, the air in coastal towns was much cleaner than in inland industrial cities, so there was a clear health benefit to living by the sea. The photo below of Scarborough Harbour, which was also taken by my father in 1963, shows smoke rising from buildings, a nuisance that was much worse in inland locations. The image also includes various other nostalgic features, such as a fleet of fishing boats and a commercial cargo ship in the Harbour!

Scarborough Harbour, September 1963

Scarborough Harbour, September 1963

In 1972, while still living in Scarborough, I bought my first copy of Railway Magazine. Given that the magazine has been published continuously since 1897, there was nothing momentous about that event, except for the cover of that edition, which didn’t mean much to me at the time.

Railway Magazine, September 1972

Railway Magazine, September 1972

As shown, the cover featured the famous locomotive Flying Scotsman, which I recognized, but I was completely oblivious as to the location. I knew that the locomotive was touring the USA, but that was all. In fact, it shows Flying Scotsman at a far-away seaside location, near Fisherman’s Wharf, in San Francisco. How prophetic for me!

(The astonishing subsequent story of how Flying Scotsman’s owner went bankrupt during its US tour, leaving the locomotive impounded at Fort Mason, can be read about here.)

The sea often featured in my childhood paintings, as in the image below, which I produced at school, at the age of 14. It purports to show a British flying boat over New York, although at that time I’d never seen New York except in pictures. (The cheap paint used in the picture has decomposed over the years. Originally, there was a calm moon shining over the sea, but now it seems to be exploding!)

Flying Boat over New York, as imagined when I was 14

Flying Boat over New York, as imagined when I was 14

A Very Significant Sea Change

In November 1987, I arrived for my new job in San Mateo, California, and found myself once again in a seaside location, albeit on the opposite coast of a different continent. I was initially quite confused, because I hadn’t been aware of the existence of San Francisco Bay, so, living on the Peninsula, I wasn’t sure whether I was looking west at the Pacific Ocean, or east at the Bay!

Nonetheless, I soon figured out the local geography, and settled down to live the remainder of my life by the sea! The 1996 photo below shows a view over San Francisco Bay from the kitchen of our house in San Mateo.

San Francisco Bay from San Mateo, 1996

San Francisco Bay from San Mateo, 1996