Building a PC - power supply

13 March 2018

Interview with

Nick Batterham - Cambridge University

Naked Scientist Katie Haylor took up the challenge of building a desktop PC with the help of Nick Batterham from Cambridge University's Department of Computer Science and Technology. Step 1 - connect the power supply...

Nick - This is the black box that most people have underneath their desk.

Katie - I can see what looks like a fan on one side, and then in the middle is a big green circuit board with a whole lot of stuff going on.

Nick - Yes, that’s right. The fan on the back of the box is to aid cooling that comes as part of the box. The big green board that you see at the bottom is what we call the Motherboard. It’s a printed circuit board about 30 cms square and it’s on this board that you connect the microprocessor, the RAM, and peripheral cards like a graphics card, for example. The motherboard enables the communication between all those components and it also allows you to connect external components like a hard disc or a CD/ROM via suitable cables.

Katie - We need a power supply, right?

Nick - Thats right.

Katie - In order to do anything we need some power, so where is the power supply?

Nick - This is a power supply.

Katie - It‘s a kind of grey box, again with a fan to make sure things don’t overheat, and then there’s a whole load of cables coming out the back of it.

Nick - Yeah. The power supply takes in the normal mains that everybody has at home converts it to voltage levels that are suitable to drive the electronics; round about 12 volts, 5 volts, and sometimes 3.3 volts as well and, of course, you need grounds too. That’s what all these different colour cables are: the yellow means 12 volt, black as ground, red is 5 volts, orange is 3.3 volts.

Katie - Can we put it in?

Nick - Sure.


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