I've got a stereo jack to Jack.

I stole off Dave's death.

Sorry, Dave on.

I'm just about to modify it to be more like one of these will carry ground.

We need to work out which one it is every guy.

So let's try loading this in now.

Nothing coming out there till now and that Let's make it.

I'm for the fi tape.

Moving error.

No, it's Dr.

You were not quite so loud.

We get that we were looking for.

Yeah, we got Q R code.

Yeah, there.

So we end up going to the fictional computer games company and you can see the games.

Netflix released a special interactive movie off the TV series Black Mirror that started on Channel four by Charlie Brooker called Bandersnatch on Dhe.

For people like me and people like Sean, who's filming this, it was set in the 19 eighties, so there's a real sense of not styled.

One thing that was interesting is that he selected one particular set of endings.

You could get to a point where the main character will be selecting a tape.

Put it into play and you would hear a noise like this on to some people, that sort of thing, that I said like modems starting up.

But for people who sort of grew up in the UK in the eighties, that was very much instantly recognizable as the loading sound for this expect from which was a computer I had as a child.

So we thought we try and load that in and see what it did.

We spent about two hours trying to actually get that to actually load in.

Basically because the volume level coming out of the Apple laptop, the world's most expensive tape recorder for the Celtics spectrum, wasn't loud enough for the set.

Expect him to lock on to the actual signal on load the program in tape.

So we thought would be an interesting thing because we haven't committed before.

We've looked at how discs worked on things to actually talk about how computers in the late seventies early eighties used standard audio cassette tapes to store data.

So you it's certainly in the UK, more perhaps, than in the U.

S.

But over here, most people be buying the sufferer on cassette and loading enough A domestic tape recorder.

I mean, they're expecting you.

Plug your standard tape recorder in Commodore 64 some of the Amstrad ones were slightly different and that they had dedicated data sets or the data quarters.

I think they called it on the spectrum plus division, which were built in or dedicated for using on the machines, which solved a few issues, as we like we had here.

Let's see how well, actually load something.

And I'm gonna use this one with the built in cassette recorder purely because of the amount of trouble that we had getting it to load reliably.

I think using the built in one overloading alpha natural shape makes the bit more sense.

Excuse the Heath Robinson.

This off the set up here.

I don't have the cave was anymore so much on.

I'm just going to rewind the tape that I said, We now let it up.

The is that expect trim.

We've covered that before.

This is the more advanced 128 k model.

The expression 48 k model.

We just come up more or less like this and say to let the program you type load, quote, approach.

It returned, and then you would start the tape on the same procedure would work on some of that.

The Commodore 64 with a few variations.

You talking slightly differently, depending on what machine it waas.

So hopefully in a minute it'll start getting some signal.

So what's actually happening now?

No longer Sam uses taping about 37 years.

What did the stripey lines mean?

The striker lines Just a visualization of the data that's coming off.

We then get program title, and it's now loading in the program.

Really?

Striping lines down here are actually a representation off the data's it's being loaded in.

Off tables are stored in an audio signal, so that noise you can hear is the day to the bits that represent the program converted into audio tones for then loaded in by the computer.

And so the program would then let it.

And he would take awhile for these programs that in the speed these things work often particularly hi, and we could sort of see that so take probably about three or four minutes for your game to load, or, more likely, if using a domestic tape recorder.

On top of the other things you get to the end of it would say, our tape loading error and after rewind, adjust the volume and start again.

Which is sort of the problems you were having when trying to load the one from the end of the Bandersnatch movie into the system.

But we did get it working there because that's it loaded, that is it ready to play nice still lighting.

So it took a while to load the game in but similar procedures, and you got similar sort of screens and you didn't necessarily get the sort of weird graphics around the back way.

That was a spectrum thing, although the Commodore 64 sometimes did similar things when it was leading self driving as well.

But this was definitely a so the feature is that expect room games now loaded.

We can barely see what's going on.

Pressing a key to start W to increase angle cue to decrease angle are in Peter Rotate the club enter to play the shot, but you just have some sort of resemblance to what you might classes crazy go.

So that's ever think about what's going on when we load something.

So what's happening is is actually very simple.

The way that the spectrum generated the signal that went out onto tape is that it had an output part of its computer, which you could either take to be, um plus five volts.

Or we could have it being zero votes on the computer could change this to create different patterns.

And if it also lays that between the two things, it effectively creates a square wave, which, if you then played it would sound like a tone that sounds familiar to anyone who waas using is that expansion.

So what the computer could do is it could alternate between a positive value and zero votes to create away from which could create sounds.

And so when he was saving the data, you've got a Siri's of bits that you can lay out one after the other C word to say about 1000 bites.

That's eight bits per buys that 8000 bits yet one after the other.

So we can write that and we need thio.

Basically, take that on dhe, send it out as an audio signal.

Now you might think Well, okay, um, I will just send of its 101010 and send it out across the way he did that.

You would send the data across.

Another computer could receive it.

But when you wrote out onto an audio cassette, you probably wouldn't be able to receive the data again.

So interviewees modulating into comfort into actual tones that audio tones like you would if you were recording speech your music and so are you also need to be able to sort of get started and get into the actual program there.

Where it starts, There ends.

Then what happens?

Data's going on on the neck spectrum.

Your program would begin with a block, all of the same frequency.

And if you look at the code for the offering system, you can see that this works out around 810 Hertz.

And when you load the program, the computer can see that, and it sees that oscillating signals about that frequency and says, Okay, I'm now coming to the point where I'm going to start loading the program and it locks onto that knows that is now expected to it at the very end of it.

There is a very specially shaped pulse, which is a different shape, then knows that it's reached the end of the leader.

So you get this leader and it knows his research, and then those that the bits that follow are going to bay data.

And so we then get a very small chunk, if my memory.

So it's about 17 bites, which is a header which describes the program.

So if we go back Thio, we want the cassette first it was when he starts to flashing between red and blue.

That's what it's locked onto the leader.

So it knows it's found the thing, and there we get this bit here, sport it for a second.

It's saying program go so it's loaded in the header on that head has told the computer that this is a program, which means it's a basic program.

So it tells you what type of fire is.

Is it, um, program basic programs that machine code, or data is its Pacific time of day deserves telling us what is.

It tells us how big it is and where it's gonna be loaded into memory, depending on what type of data it is.

So it blows us all in the header on When you typed load, you can either say load quote, quote, which will load in any file.

Or you could load a specific file that, if it doesn't matter static way into it, finds the next header that tells you what it is that there's another bite here hidden in the header, which tells us whether it's a header or whether it's stage.

And then we get another a bit of leader again off the same tone.

But it's much shorter and again exactly the same purpose.

It Nate was a computer to get into.

Think with this.

You get that sync pulse at the end to say this is finished.

If we restart it, it starts to load in the leader, and now it's loading in the program.

In this bit of the section, it could be a various length we don't know, and it's just the data or the program.

So these two sections here they're not made up a one tone, but they're made up of two different tones, and so you either have a tone that is sort of this length, so the shape or you have one, which is twice as long.

So we send this.

If it's zero, we send this.

If it's what, and so what?

We get one of the way form and what the computer can then do is what he's loading it back.

If you get the bowling levels right, it takes the audio signal, which isn't really, which is a beta for lots of first, more fragments of different frequencies in the zero or one to make it.

The programs is loading the back end.

He can count the number of edges it sees within a specific time and work out whether there's enough evidence for you to be a zero or there's enough veggies for it to be a one and then reconstruct the data.

This being loaded it on this a few bits of parity in there and other things so that you can check whether it loaded all correctly or not when it gets to the end.

But it's unable to sort of process.

The data is the signal's coming in saying right, I've seen this edge of seeing the centrist in this edge.

That means it should be zero.

I'm like a zero into memory should be a war no one that was wanting to memory and load the data back in.

Now, Obviously, when you're doing this, you want to make sure that your system is stable and one of the problems with cassette tape is it is a recording medium.

It wasn't that stable.

If your battery started too often, the pitch of the music you're listening to would drop because it was linked to the power and so on.

And that was fine for music.

Brest attack was imperceptible.

He wouldn't notice there.

Wow and flutter as it's called for a computer program.

That's a real problem.

So what people did Well, what single I did when they designed this is they chose values for how long those pulses were going to be, whether it's zero or one to be such that if there was wound flutter, the computer would be out okay.

But if it was slightly faster or slightly slower and still be able to cope with the data, Commodore actually went slightly further.

If we turn on the C 64 they actually stored two copies of the program, one after the other one they recorded so when you saved your program out, it would write out the program and then immediately after that, as a separate block would write out the problem again.

Some of the check me using a series of long courses in short courses to represent zeros and ones.

So when we load in a program on the Commodore using it data set and it will start load again, it would load the program in.

And if there's any errors in there, would make a note of where they were within the program.

And then when the second coffee is played through, it could load in, hopefully correctly.

From that point, the bits that have gone wrong on sort of correct the arrows and was able to sort of recover your program.

You mentioned that they're given a memory address to then things just sequentially follow on.

From there.

It seems to me that memory dresses a long bit of data in its memory, just describes where the first bite goes on.

So what happened is that you get a memory address on it, would say loaded in here.

Let's say it was a screen on the select special.

It's a loaded at 16384 in memory, so that computer would load in the 1st 8 bits one after the other, form them into a bite in one of the registers and then write that back, bite out into memory at 16384 then loaded the next eight bits from tape and like that out into memory.

But it's 16385 and so on until it loaded in the whole bit of data.

And you have any bites?

The work, the case with Screen 6912 and it could load them into the right places.

Interestingly, these loading when saving, which means we're completely written in software.

And if you actually look at the implementations in the wrong chips, each path that the problem could go down has been correctly, sort of worked out to take exactly the same number of CPU cycles, so that when it produces, the pulse is between the two.

They're all of exactly the same length, so they're all of exactly the right frequency, and you produce the data that you need, and when it's loading it again, it's counted so they can knows exactly how many edges have been found in a particular point in time, they have to turn things like interrupts off.

It's a bit like when we talked about writing software for the 2600 these routines very carefully written.

The downside of them is both on the C 64 on the set expected.

Mr.

They took a long time to lead in the program.

And so what people did, particularly commercial software houses when they're writing software, is that it would write fast.

Loaders are turbo loaders, and all they do is they rewrote the routines that would load in the program.