>>Sean: You’ve got this guy, Bill Tutte, with his
team of people – or the team of people who he was working with – and they have cracked
this code. Why do they need computers? Where did Colossus come in?
>>DFB: Colossus came in because
the sheer amount of counting that you had to do was enormous. You were
basically, in the end, looking for the occurrences of dots (or zeros) in, well
41 * 31 * 5 times whatever [settings to try out] … You know, you might be able to afford to get the
whole Research Section doing just one little bit of it, but day in day out? All
you wanted to do was to look for patterns and count out the number of
zeros within them. And you need a computer! It doesn’t matter if it’s a
special-purpose computer – which Colossus was. When they first realized this they
tried to go back to Enigma-type technology: “Oh! we understand about relays
and uniselectors. let’s build something electromechanical”. It was called Heath
Robinson, and for those of you in North America Heath Robinson is the direct
[UK] equivalent of Rube Goldberg. They were both cartoonists that drew
impossibly complicated electromechanical machines, and made cartoons, out of them
So, there’s this huge amount of stuff to be counted up but electro-mechanically,
when they tried to do it, it couldn’t go fast enough. It would take days. And they
tried to speed the machines up and they just went up in blue smoke. And
eventually I think Alan Turing had worked with Tommy Flowers from Dollis
Hill GPO [General Post Office]. He’d worked with them for some aspects of the Enigma
decode but as we know [for] Enigma electromechanical was just about OK.
But Turing said: “Why not let’s get in Flowers for an opinion and Max Newman
who was by then head of Research Section, said: “All right, bring him in and we’ll have a chat. And
Flowers took one look at it and said: “You will never get it fast enough to do what you
want electromechanically. Forget it! We’ve got to go electronic and use valves”.
And of course there was a huge [outcry]: “Flowers are you off your head?! We all know valves, they go ‘bang’ every few minutes! They’re not reliable.”
I think I’ve said this before [but] I’ll say it again: Tommy said to them “I’ve been doing
research on use of thermionic valves in telephone exchanges and I can tell you
they can be remarkably reliable so long as you never turn them off”. And it’s
particularly the heaters on the cathodes. If you bring those up to voltage very
quickly so they instantly go red or white hot the filament will [often] go ‘bang’,
but if you bring them up very carefully, from dull red to bright red, and all that…
And then, at the end of the day, don’t switch them all off. Lower the voltage and do
that very very carefully. You will minimize the number of thermionic valve
blowouts you get and so, basically, the message was ‘Never ever turn them off and
it’ll be fine’. And in the end it was. And the electronic speeds were just about
enough. But it still took … a typical run on Colossus to discover Initial Settings
on a pair of wheels might take 10 minutes, something like that. And you’ve
got to do that for five different pairs. So, y’know you’re taking about an hour
to work out settings, if you didn’t know them alread. Standing Orders said: ‘You
must never take more than two hours’. If you haven’t got it sorted by then, on the
settings, give up [and] go to another message. But then, if you knew the settings but
didn’t know the wheel patterns that was a huge amount of effort [that] was needed. In
fact Frank Carter reckons 10 hours of Colossus time to establish what the
patterns of 1s and 0s were on the wheels. Now you’ve realized why they
ended up with 10 Colossi at Bletchley Park. They got a huge amount of work to do.
And you mustn’t also run away with the idea that Colossus could do absolutely
everything. It couldn’t. The great majority it could, but it relied on this
slight statistical disparity, there were always more 0s than 1s. And look
for what [wheel] setting make that happen. But just occasionally a rogue message
would come in where it just happened to be 50:50, and there wasn’t a skew or a bias. And then you have to throw that one away
and say: “We’ll come back to that later”. So it wasn’t 100% but it was good
enough to make a decisive difference to the war. Yes, it seems weird doesn’t it
that it’s not 50:50 between 0s and 1s?, in a regime where we’re doing
exclusive-ORs. Well, what you’ve got to remember is if you exclusive-OR
something with itself you get a bunch of 0s. But whatever it is, if you exclusive-OR
all those together, if they’re identical the exclusive-OR, on a character basis,
will be five 0s and to make those show up at Bletchley they denoted it
with a /, if you remember. OK, well, that’s all very well but that …
so how would that lead to a bias, a skew ? Answer: in many many languages, not
the least German and not the least English which, as we must remember is a
Germanic language, you get doubled letters, OK? So, Sean, if I say to you – I’m
guessing – the probability of ‘z’ in English is 1/100 what’s the probability of
getting two z’s? 1/100 times 1/100?>>Sean: Well, hat would be the mathematical answer
>>DFB: Yeah! Yeah! if they’re all independent it will be 1/10000. But they’re not! Double ‘z”
is far more common, even in English let alone in German. than one in 10,000.
Really, you know, ‘dazzle, ‘puzzle’, all these kind of things. It’s not massively
common, as a bigram, but it’s more common than the base
probabilities would indicate. Double p’s as well: “happy, slapping, flappy”. All these
kind of things. So character doubling was one of the vital components of saying
that if you look on a certain stream and it’s a 0, and you look on the adjacent
streams from 2 to 5 and it’s a 0 as well, then it’s a null character. And that
could have been generated by having one thing exclusive-ORd with it’s identical
thing. So, on a bitstream basis they adapted that and said the reason we are seeing more 0s is that if you slide these
bitstreams over each other by one bit and exclusive-OR, them you’ll find that
double-letter occurrences lead eventually to more 0s coming out than
1s, because on the nature of exclusive-OR, – if something is the same as something
else and you exclusive-OR it – it gives 0s not 1s. So, it’s a bit rough and
ready and hand-wavy, there’s more to it than that but that is just one example
of how the language structure itself can do you in. And it’s reported that the
German cryptanalysts realized that this would be a weakness of the Lorenz cipher
but they said: “We’re not to worry, it would need you to build a machine and
they’ll never be able to do that. There’d be so much data it will kill ’em!
You’d need roomfuls of people and even within a month they wouldn’t do it. But
what they didn’t foresee was the advent of machines with electronic speeds, not
just electromechanical ones, and that could just about get on top of it.

Why Build Colossus? (Bill Tutte) – Computerphile
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52 thoughts on “Why Build Colossus? (Bill Tutte) – Computerphile

  • September 14, 2018 at 12:35 pm
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    1st

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  • September 14, 2018 at 12:36 pm
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    I love all the videos with professor Brailsford!

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  • September 14, 2018 at 12:37 pm
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    Such an interesting topic and such a calm and intelligent man

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  • September 14, 2018 at 12:37 pm
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    Because building Colossus increases trade?

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  • September 14, 2018 at 12:40 pm
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    Interesting!

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  • September 14, 2018 at 12:44 pm
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    Look how times have changed: from "Never turn off the computer" to "Have you tried turning it off and on again?"

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  • September 14, 2018 at 12:48 pm
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    Professor Brailsford is the boss!

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  • September 14, 2018 at 12:50 pm
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    Wow, I know a lot about ww2 but I was oblivious about this machine and it's counterpart it was built to crack. Thanks for the upload.

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  • September 14, 2018 at 12:53 pm
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    Legend…

    And Tommy Flowers, being a practical man, not just theoretical, was spot on… Valve last for years if you just leave them running.

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  • September 14, 2018 at 12:59 pm
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    Because they are good against light units

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  • September 14, 2018 at 1:02 pm
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    Dr. Forbin's answer was quite sufficient, thankyouverymuch.

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  • September 14, 2018 at 1:09 pm
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    You shouldn't, they get easily countered by the zerg's corruptors.

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  • September 14, 2018 at 1:16 pm
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    I'd listen to Brailsford talking about pretty much anything. Keep him on as long as possible 🙂

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  • September 14, 2018 at 1:54 pm
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    Pizza! 2 Z

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  • September 14, 2018 at 2:11 pm
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    heh, I have something to attest to the power of tubes being gently heated and kept at slow-ish smoulder…

    The Hammond Novachord :3

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  • September 14, 2018 at 2:20 pm
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    So how did they go about estimating which letter the exclusive ORs represented? A neophyte here, thanks a lot!

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  • September 14, 2018 at 2:38 pm
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    I can listen to this guy forever

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  • September 14, 2018 at 4:21 pm
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    … To crack the code… Duh…

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  • September 14, 2018 at 4:28 pm
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    Why? To play Numberwang, of course.

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  • September 14, 2018 at 5:03 pm
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    I've just realized why I love hearing Professor Brailsford speak — he sounds just like Winnie the Pooh!

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  • September 14, 2018 at 5:14 pm
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    Is there anything better than a Brailsford video?

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  • September 14, 2018 at 5:24 pm
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    Interestingly, in all the books I have read about Alan Turing, Bletchley Park and so on, there is very little connection mentioned between Alan Turing and Tommy Flowers, and I believe Turing had long moved on to Hanslope Park (early 1943) to work on voice encryption by the time Colossus actually became "Turing Complete" and properly programmable with decision branches and loops. So we end up with the man who defined what a computer is, and the "first" (yes, Konrad Zuse etc, I know) programmable electronic computer in the same place, but with seemingly no link between them.

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  • September 14, 2018 at 6:39 pm
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    I like this guy

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  • September 14, 2018 at 6:54 pm
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    Thanks again Professor Brailsford

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  • September 14, 2018 at 7:09 pm
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    could just have droped the double leters in their mesages

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  • September 14, 2018 at 8:04 pm
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    I love listening to him.

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  • September 14, 2018 at 8:58 pm
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    Did you never even see The Forbin Project, you fools? You've killed us all

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  • September 14, 2018 at 9:04 pm
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    Wow. I mean they could've simply prohibited double characters. You would be able to properly understand the whole message once decrypted but would get rid of this weakness by the cost of an order…

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  • September 14, 2018 at 9:18 pm
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    Professor Brailsford is a pleasure to listen to. Please give us more! =)

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  • September 14, 2018 at 9:43 pm
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    For our yank friends, thermionic valve is a vacuum tube.

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  • September 14, 2018 at 10:43 pm
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    If only the Germans had been broadcasting in lipograms excluding double letters, lol.

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  • September 14, 2018 at 10:45 pm
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    And now… you could probably do it in a crappy Arduino, let alone a Raspberry!

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  • September 14, 2018 at 10:53 pm
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    What? So if they "transmited" the "mesage" with purpose "mispeling" by removing the double chars… the "mesage" would be readable but not crackable?

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  • September 15, 2018 at 1:03 am
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    When i was an industrial electrician in a factory that ran 24/7 365 days a year, we used to hate shutting down equipment for maintenace. There was about a 50/50 chance that one of the electromechanical parts in the system would fail on startup.

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  • September 15, 2018 at 2:54 am
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    That's NUMBERWANG!

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  • September 15, 2018 at 7:40 am
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    I Love all of computerphile videos

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  • September 15, 2018 at 6:50 pm
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    I always love listening to him, doesn't matter what the topic is. Such a treasure.

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  • September 15, 2018 at 8:52 pm
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    This is similar to X-Ray sources for crystallography (Cu, Mo, etc.)

    There is a working-voltage and a standby-voltage and these instruments (to be used by researchers) is only to be turned off for maintenance or long pauses in work schedules

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  • September 16, 2018 at 12:34 am
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    This is one thing assembly language programmers usually learn. Back in the 8 bit microprocessor days, you used to look at how many bytes an immediate load used to take, like LD A, 0 on the Z80, and how long it took to execute, and compare that with a similar operation like XOR A, A, a lot of times it took less time (clock cycles) or less space or both to do the XOR. As long as you knew this as an idiom, or made code comments, it didn't reduce readability/intelligibility.

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  • September 16, 2018 at 7:45 am
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    I love the WWII and code breaker talk. Please keep him talking about this.

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  • September 16, 2018 at 7:53 pm
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    Imagine the change that would have happened if someone took a simple Raspberry Pi back in time to the scientists/arithmeticians working on this stuff.

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  • September 18, 2018 at 4:42 am
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    I wonder what the clock speed was for that thing. A few Hertz? 100?

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  • September 20, 2018 at 7:54 pm
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    We should never have insisted on 'stickstofffreie Schifffahrtsspeziallagerrechte'!

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  • September 24, 2018 at 7:35 am
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    Please interview Brailsford on Apple. Just want to hear his thoughts. Leaving this comment here, barrel completely unloaded. You know it's the right thing to do.

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  • September 27, 2018 at 2:51 am
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    Awesome video as always. From the video, "Tommy said to them, I've been doing research on use of thermionic valves in telephone exchanges…" Valves had been used for since 1915 to amplify long distance calls. The genius of Tommy Flowers was his research into switching calls electronically. He was way ahead of his time… and sadly under-recognized for his contributions.

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  • September 30, 2018 at 5:25 am
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    would the Germans have known character doubling was an inherent flaw in encryption? perhaps a "drop one letter from all double letter words" directive should have been implemented!

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  • October 16, 2018 at 4:47 pm
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    I could never wrap my head around that code could be cracked by statistics. but now i can thanks to him!

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  • October 18, 2018 at 3:30 pm
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    It is really funny that I saw the your Enigma Videos about a year ago, decided to make it the topic of my seminar paper (the exact Topic is 'deciphering machines at Bletchley park') and just when i came to the chapter about the Tunny and Colossus I found this video uploaded not long ago xD

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  • December 11, 2018 at 1:59 pm
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    Absolute legend

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  • December 18, 2018 at 1:27 am
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    I use valves (tubes in my case) all the time. They are still quite common in medium to high power transmitters. The same holds true, we like to bring the filament up slowly using a variac or even a built in so called soft start circuit. They are highly reliable if treated properly and can be abused much more so then transistors in similar applications. As the old saying goes a MOSFET is one cycle from exploding at all times! Don’t get me wrong I don’t want to go back but it amazes me how fragile people thought tubes could be and my experience is exactly the opposite

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  • April 7, 2019 at 5:55 am
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    My uncle worked at Dollis Hill, with Tommy Flowers.
    He never spoke of his work. (Wretched man!)

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  • August 21, 2019 at 1:33 am
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    His heat sync speech on tubes is still valid today on all electronics or breaker boxes.

    Reply

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