Computers from the past

How does a computer work if it doesn't have a processor?
13 March 2018

Interview with 

Jason Fitzpatrick - Centre for Computing History, Cambridge

Elliot Computer

Elliot Computer


For many of us, a high resolution, colourful screen is a key part of any computer - be it a smart phone, laptop, or desktop PC. But this wasn’t always the case. With the help of Jason Fitzpatrick from the Centre for Computing History in Cambridge, Katie Haylor took a trip back in time to meet a few computers from the past...

Jason - My name is Jason Fitzpatrick and I am the CEO here at the Centre for Computing History.

We look at more of the home computing, the way computers started to become part of our lives. And we’ve got a machine back there from 1963 which is called the Elliott 903. It’s a computer that doesn’t have a CPU - no microprocessor.

Katie - To be honest, it doesn’t look, to me, like a computer at all. It’s an enormous big box that looks a bit like a fridge or something and inside there’s racks, and racks, and racks of electronic components. Are they transistors?

Jason - Yes, they are. They’re transistors, yep.

Katie - How does it work; what does it do if it has no processor?

Jason - That’s why it’s on display; this is an interesting story. Most people think a computer has a microprocessor which, obviously, modern ones do. But, what is a microprocessor? It’s simply a semiconductor that has thousands and thousands, millions, in fact billions today, transistors on it all shrunk down into silicon and then they form the processor, the brain of the machine. Actually, if you go backwards, then you could theoretically make a computer just out of the transistors themselves, and that’s what this machine is.

Katie - What are the transistors doing?

Jason - Simply switching on and off. Computers, most people know, work on binary - ones and zeros. In fact, we say ones and zeros, but to a computer it’s not even ones and zeros. It doesn’t understand what a one or a zero is, it understands whether there’s an electrical signal and no electrical signal.

Katie - So off/on?

Jason - Exactly. Off and on. This computer has, I think, about 2½ thousand transistors in it that make up the processor. It’s kind of all a processor, the whole thing and if you shrunk all those transistors down, that would make a microprocessor that we know today.

From here, the transistors in the Elliott, they were packaged into small chips - logic chips - and we had maybe had 100 transistors on a logic chip. But, as we got better and better at making those logic chips, we can get more on there and then we start to have an entire computer, an entire Elliott, on one chip. That then allowed us to do more with that so you could have lots of these chips and make a more powerful machine.

Katie - What have we got here then?

Jason - This is our 80s, we call it 8 byte 80s. And the one I’m going to choose is the Sinclair ZX 81.

Katie - It is tiny. It’s just a black square with a tiny, tiny keyboard on it and then there’s a monitor which looks incredibly old school.

Jason - It’s a television.

Katie - It’s a TV? Oh wow, okay.

Jason - You had 1k of memory. You can’t even send an email these days in less than that.

Katie - Wow!

Jason - It had all of the colours as long as that was black or white. It had no sound and it was brilliant!


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