How Computers Really Work

Author : Guest Blogger
Date : September 23, 2018

The first time you saw a computer, it probably managed to convince you it was pretty smart.  Computers can do all kinds of amazing stuff like add up numbers really fast, draw pictures, make music, and some even control robots.  That’s all really cool, but you want to know a secret?  Computers are actually not very smart at all.  In fact, a computer can’t really figure anything out for itself, it has to be told how to do everything.

 

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There are a few things that make you, as a human, actually better than a computer, even though most computers are faster at performing individual tasks than most humans.  Check out this chart of things that will help you decide if you’re a human or a computer:

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Having the abilities of a computer would be great, but it’s still better to be human.  One simple way to think about it is that computers are really good at things humans find difficult, and they’re actually quite bad at things humans find easy.   That means computers aren’t really a lot different from other tools:

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If a robot was chasing you, it’s possible that it might be able to move faster than you can, but you could still get away by climbing up a tree.  Even if the robot also has the ability to climb a tree, you can still get away because you are much smarter than any robot ever built.

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Early computers did not need electricity to operate, but they were very limited in their abilities.  All modern computers require electricity, which can come from mains power (where you plug a cord into the wall), batteries, or even solar power.  New technology is being developed which may make all of these power sources obsolete as requirements for computers, but it’s still not a reality in 2016.

 

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Regardless of where the electricity comes from, it enters the computer’s circuitry via a device called the Power Supply Unit (or PSU).  In a desktop computer, this is a large and heavy component to make it reliable and thermally efficient.  In portable computers, the PSU can be much smaller and lighter, because the input power is much lower and portable computers are also less powerful than desktop computers.

Electric current flows into the PSU, where the voltage gets massively stepped down to the correct voltage for the computer, a process called transforming the electricity.  The transformed current goes from the PSU into the computer’s motherboard.

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A motherboard is a big piece of plastic with metal tracks painted onto it by robots.  Then electronic components like resistors, transistors, and—most importantly—I/C chips, are added to the motherboard to control how the current flows around the circuit.

The motherboard looks a bit like a city, with metal tracks looking like roads and the other parts looking like buildings and houses.  Electrons travel along those tracks to get to where they need to go, just the same way that kids ride a bus to get to school.   So engineers call the path that electrons take a “bus”, because that’s how the electrons travel around the motherboard.  Well actually the electrons don’t move fast enough to do much at all, they actually just pass an electromagnetic field along the path, but it’s a lot easier to understand if we just imagine the electrons themselves moving.

When the electrons leave the PSU, they all have a value between 5 and 6 volts.  Each electron represents a bit (binary digit, which we’ll discuss in more detail in another article), and a group of 8 bits—which is the smallest logical unit a computer can process—is called a byte. When a bit has more than 5 volts, its binary value is considered to be 1.  When it has a value of less than 0.5 volts, its binary value is considered to be 0.

So each byte that leaves the PSU has a value of 11111111 in binary (which translates to 255 in the decimal number system that humans prefer).  As the byte travels around the motherboard, things will happen to it that can change its value from 255 to some number lower than 255.  You probably already figured out that the smallest value of a byte is 0 and the highest value is 255.

If absolutely nothing happens, the byte will travel all the way around the circuit back to the PSU, and the value will stay at 255.  Every time the value of a byte is changed from 255 to something else, that indicates that an event occurred.  An event is when something on the computer changed, like for example that you pressed a key, or that the a software instruction updated something.  When an event occurs, a part of the computer called the BIOS generates a response called an interrupt.

As you would have guessed, this means the BIOS interrupts the CPU (which is already really busy) and passes on the information that something important happened.  Here’s a cartoon impression of how that happens:

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Well, that was a fun way to get an idea of how things work, but of course the reality is much more complicated than that.  What’s important to understand is that everything in the above scenario would have  happened millions of times per second.  Also it never happens one byte at a time like that.

Anyway, to break it down to the simplest possible terms, how a computer works is that electricity gets divided into two different voltage levels which can be used to represent binary numbers.  Those numbers can be combined in all kinds of different ways to help the computer understand what it is supposed to be doing at any given moment.  And when there’s no voltage at all, the computer just stops working.

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