[Lucien Nunes]

2. Binary memory. How is data stored? What's a bit and what kind of space does it take up? What's actually different about a bit that makes it a one or a zero?

In all computers that you might see operating, it happens in microscopic scale, invisibly, by the movement of a few electrons. You can learn about this at a computer museum but it's impossible to see it actually happening. Or is it?

Before electrically-readable and writable binary memory was in general use for computation, it was in use embedded in control systems. For example, from the beginning of the 20th century, the London Underground was transmitting encoded train descriptions that were stored word-wise on a device called a drum receiver. It's got huge great 'bits' that pop in and out and are easily human-readable. It's very easy to see it read and write them, and a great introduction to all the core ideas and principles of binary memory. Where can you see one working? Answer, very occasionally at the London Transport Museum depot open days, maybe nowhere else. And of course, if you wanted to learn about how your mobile phone works and how your laptop stores data, you would instinctively make a bee-line to a transport museum, wouldn't you? And when you got there and asked about the 'binary memory thing that you can see working' they wouldn't know what you were on about, because to them it's a piece of signal equipment to be demonstrated as part of signalling technology. But it's more than that, it's a direct precursor and excellent demonstration of some of the principles of what is going on in everyone's pocket 24/7.

We don't have a drum receiver in the MEET collection but we have another good one: The Compton piston selector. It's the memory that stores programmable stop combinations in some very large organs from the late 1920s, and also theatre lighting consoles up to the 1950s that Compton made. Its visual resemblance to the die of a 1970s EPROM is uncanny but it's macroscopic, you can see it mechanically juggling the contacts into the '1' slots and the '0' slots as you write to it. Once you've got an understanding of the word-wise construction and the relationship between addresses and data, it's a simple step to understand that in the memory IC, electrons are being moved back and forth instead of springy wires.

So how does this translate into an exhibit?

Visitor-operated keypad allows simple text messages to be typed in, stored, and recalled onto a large LED display. The memory unit is right there in front of you with a perspex front and you can watch it work from literally six inches away, but you can get a really close-up view on a screen connected to a miniature camera inside that shows a huge display of just a few bits, with overlaid text that shows what the position of the parts means in terms of the data stored. If you don't want to use the hardware keypad you can scan the QR code on the exhibit and send it a text message to store and recall.

OK, I hear you say, you could custom-make an interactive to demonstrate that with all modern stuff, like a regular museum. Sure you could, but it would cost a bomb to have commercially designed and built, when I've already got the Compton units working in the stores and could put the money towards something else. More importantly, you can see the very same piece of machinery in the back of one of our working lighting consoles that forms part of a demonstration itself. When you see it there, you will think, 'Aha, I know what that is and how it works, it's like a flash memory but bigger, it must be storing the lighting changes'. You start to get a sense of achievement, because the learning experience with the interactive exhibit connects with the real world, rather than being a sterile, artificial construct.

When you go into the cafe you'll find the juke box standing in the middle of the room with a perspex back on, with arrows pointing at various parts of the mechanism. No interpretation, it's a puzzle. What's arrow No.3? 'Aha,' you say again, 'I know what that does, it's like the other memory mechanism but different.' When you select a record, it pushes a pin up, and when it plays, it pushes it back down. You start to follow paths and make connections between things you've played with and others that work similar ways, and so you build and cement your understanding.

So the jukebox is an educational tool too. So many things to watch going on inside. And quelle surprise, it's a ready-made, customer-friendly piece of vintage tech you can interact with, designed for heavy use and placed in its natural setting. The only thing we have to to is make a perspex back for it.

Back to that point I made at the end of the previous post:
The juke box, lighting console, organ piston memory and drum receiver are all parts of the same story that leads into home computing, which might be what brought you along to MEET in the first place. But can you play a record on a juke box at the London Transport Museum? That's our USP. We hooked you in and got you thinking about different things, and therefore learning.