5.1 Peripherals
This section will introduce you to a range of peripherals connected to a typical desktop PC, and show you how the computer engineer and computer scientist each view the communication between the peripherals and the main PC.
Activity 11 (exploratory)
Below is the video that you need to watch for this activity. This consists of the introduction and first section (entitled ‘Outside to inside – peripherals’) of the ‘Inside the box’ video. You will need your computer’s speakers or headphones to listen to it.
Download this video clip.Video player: Inside the box: introduction and section 1
Transcript: Inside the box: introduction and section 1
[Graphic title: Inside the box]
[Music – duration 00:12]
Spencer Kelly
Most of us use computers in our everyday lives, and usually we’re happy to think of them just as tools for word processing, playing games and so on. But in this video we’re going to go inside these faceless boxes, and we’re going to think of a computer from two extreme viewpoints. We’re going to look at the physical hardware from the point of view of an engineer, and then we’re going to consider the theoretical point of view from a computer scientist.
Now, you can think about a computer in many different ways. Whatever you do, it’ll be between these two extremes.
So here’s a typical setup that you may have at home. Let’s consider the physical viewpoint first, that of an engineer. Dr Darien Graham-Smith is Technical Editor of PCPro. Hiya.
Darien Graham-Smith
Hi there.
Spencer
OK, take a look at this. What do you see?
Darien
Well, as you say, I’m interested in the physical hardware. I think about the components that are in this computer that might make it suitable for maybe to be a general-purpose desktop computer or maybe a specialist computer such as for controlling the engine of a car. Obviously this is a desktop computer, so I might be interested in how much memory it has or what connectors it has for connecting to different peripherals.
Spencer
OK, Darien, thank you. Hold it there, we’re going to bring in the computer scientist now. Dr Parisa Eslambolchilar is a computer scientist and a Lecturer in Computing at Swansea University. Parisa, hi.
Parisa Eslambolchilar
Hi, Spencer.
Spencer
What interests you about this particular computer then?
Parisa
I’m interested to find out how to solve problems with these computers. I’m rarely interested in the physical form of computers, but I’m interested to find out what capabilities these computing devices have and how to tell this computer – these computers to do things efficiently.
Spencer
OK. Would you mind showing us?
Parisa
Yes. When I look at this computer, what I see is a big box called ‘computer’. And inside this box we have a processor, which is capable of carrying out instructions. We have memory, which is capable of holding data and instructions later the processor is going to perform. And we have input/output devices as described by Darien.
Spencer
And so that’s how the computer talks to the rest of the world.
Parisa
Exactly. These three bits are communicating with each other, and these are called data or instruction buses.
Spencer
So you’re interested just in the arrows. You don’t care what the arrows are made of. Darien comes in and says we can’t use ink, we’ve got to use copper or something else.
Parisa
Yes. This is my generic feel when I look at any computing device. A processor, memory, input/output devices.
Spencer
So you’re not interested in the make and the model.
Parisa
Not at all.
Spencer
As long as they’ve got those bits …
Parisa
Not at all.
Spencer
… you can do your job.
Parisa
Exactly.
Spencer
OK. Right, it’s time to look at this computer system in detail. We’re going to start with the components that are outside the box, then we’re going to go inside and we’re going to dismantle what we find in there. Now in doing this it’s very likely that we’re going to damage or destroy some of the components inside the computer. So please don’t try this at home. If you do open up your computer, remember to disconnect it from the mains first and remember that power supplies can store power for quite a long time, so treat the inside of a computer with care.
[Graphic title: Outside to inside – peripherals]
[Music – duration 00:08]
Spencer
Now, we’ll start by looking at the external devices that are plugged into the system box: keyboard and mouse. Whip the plugs out of the back. Darien, what do you find interesting about that little fella?
Darien
(Laughs) Well, not an awful lot. This is a fairly standard mouse and as you can see it’s got a standard connector. This is a PS2 connector. You move the mouse, it generates an electrical signal, that goes through this plug and into the computer.
Spencer
OK. And how about – don’t you just love cables? – the keyboard.
Darien
Yes, well, once again this is a standard keyboard, I’m sure this’ll be familiar, and it’s got a standard connector. In fact, that’s the same standard. That’s another PS2 connector, though it’s colour coded so you don’t get them mixed up. Press the key, generates an electrical signal, goes through the plug into the computer.
Spencer
Both devices talk to the computer using exactly the same type of plug, then.
Darien
That’s right, yes, they’re fairly simple devices.
Parisa
Thank you, Darien. In my view, mouse and keyboard are both input devices.
If you go back to the initial drawing I had to present a generic model of a computing system, mouse and keyboard are going into the box presented as the input/output or peripheral devices.
Mouse and keyboard are both generating electrical signals which represent symbolic information such as the key pressed or the mouse movement. These two devices are continuously capturing the data and then entering them into the computing system where it can be processed later.
Spencer
So different signals mean different key presses, different button presses, different movements, the computer will do different things based on those signals.
Parisa
Exactly.
Spencer
Yeah. Right, we’ve done input, let’s do output. Darien, the monitor.
Darien
Yes, the monitor. This here is a 19-inch flat-screen model, a fairly standard part of many desktop setups, and it connects by another standard connector. This is called a DVI connector. It takes the electrical signals from the computer, relays them to the screen, which then displays them as images. That’s what I make of it.
Parisa
In my view this display is just an output device, and I can actually take the plug back to the peripheral box and represent it as an output port.
I’m interested to know what symbolic information or instructional data I need to send to this device to actually make it display the data I want to, and I’m not interested to know what kind of display it is or what kind of connector it has.
Spencer
So the information that comes out of the processor needs to be turned into something that we humans can read on the screen.
Parisa
Exactly.
Spencer
Right, that’s the monitor. Over the other side we’ve got a printer. Darien, just a straightforward output device?
Darien
You’d think so, wouldn’t you? I mean, you send your pages to the printer and it prints them. But sometimes the printer needs to talk back to the computer, for example to say it’s out of paper. So there’s two-way communication going on there.
Spencer
This is an input and an output device.
Darien
That’s right.
Spencer
OK.
Darien
And it happens over another standard interface, this time USB.
Parisa
Thank you, Darien. I put back this cable on the peripheral device box.
In my view, printers are interesting devices with interesting behaviour. They can interrupt the main computer at any time. If you think about an example in real life, they can be like a scenario of reading a book and the doorbell rings, you bookmark the page you were reading and you answer the doorbell, come back and resume the reading from the place you paused.
Spencer
So that’s a fairly simple interruption then. The computer’s the one reading the book, the printer is at the door, and then it can just stop what it’s doing and then come back and resume it afterwards. That sounds pretty simple.
Parisa
Exactly, exactly. But this is a simplest scenario, we can imagine for responding to an interrupt. But imagine a different scenario – for instance, you are juggling and the doorbell rings. It’s not as easy as bookmarking the page.
Spencer
You can’t leave them hanging there while you go to the door, yeah.
Parisa
Exactly. So what can you do? You can either shout to the person at the door and say wait, or you let the balls fall on the floor and then you go to the door and come back and restart the juggling.
But it’s not always as simple as this scenario. How about responding to a fire alarm? What happens if you’re juggling and the fire alarm goes on? Can you respond to that in the same way as you responded to the doorbell?
Spencer
So you’re interested in looking at responding to different types of interruptions in different ways and possibly having to restart more of the process afterwards depending on how you left it.
Parisa
Exactly. So developing models of computing devices to respond to interrupts efficiently is a challenging subject for a computer scientist.
Spencer
Now, when we were talking about the connectors, one word stood out for me – especially from you, Darien – and that’s standard.
Darien
Yes. Standards are what make it possible for the computer to talk to all these different devices. The standard will define the physical size and shape of the connector, and it will also specify the power requirements and the sort of electrical signals that have to travel back and forth.
Spencer
OK, and these standards are available to all device manufacturers?
Darien
Absolutely, yes. And that makes it very easy. I can go to a shop and I can buy a new monitor or a new printer and I can be confident that they will work with my PC.
Spencer
Parisa, are standards important to you as a computer scientist?
Parisa
Yes, I do use standards but they are not the same standards as engineers use. I work with symbolic data and information, and I’m interested to know how computers store or manipulate the data. So I need to make sure there is a common interpretation for these symbols when I transfer the data from one device to another device.
Spencer
Right, so if you bought a new monitor, different make, you need to guarantee that it’s going to show the same information.
Parisa
Exactly.
Spencer
So we are going to hear the word ‘standard’ an awful lot more. You have been warned.
Just one more device to get rid of first. Darien, smile.
Darien
Ah yes, the digital camera. Well, of course, once you’ve taken your photographs you upload them to the PC via a standard connector again, USB.
Spencer
Surely not.
Darien
Oh yes.
Parisa
For me this is only an input/output device. I can put this USB cable in the peripheral devices box.
Spencer
OK, good, and let’s just lose this cable as well.
Darien
Yes, that’s perhaps the most important standard of all because without that one the computer can’t do anything.
Spencer
Now surely we’re all in agreement on that one.
Parisa
Well, not really. For me, it only makes the hardware work. I can still reason, I can still solve computational problems or develop the theories which can be used for the computation later …
Spencer
All without electricity.
Parisa
… without electricity.
Spencer
OK. So, as I understand it, as an engineer you’re looking at these external devices as having standard interfaces that match the standard interface on the system box. Yeah?
Darien
That’s right.
Spencer
And as a computer scientist you’re thinking about these devices as a way of transferring standard symbolic data into and out of this chap here.
Parisa
That’s right.
Spencer
Excellent. Go on, try it.
Parisa
Thank you.
Spencer
You’ll love it. Electricity. Brilliant.
Inside the box: introduction and section 1
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