What your garage door opener has in common with Internet addressing

Have you ever owned a suitcase or attache case combination lock? (click the picture on the left for a larger view)

How many different combinations are possible with that?

Well, if there are three wheels, you have 1,000 different combinations:

0-0-1, 0-0-2, 0-0-3, 0-0-4…and so on.

Ever own a garage door opener? You know — the kind that comes with two remote control units, right? Did you ever consider that your neighbor could open your garage door with his opener? It could happen, if his remote control was set (on purpose, or by accident) to the same combination as your garage door opener.

That’s right — your garage door opener can be set (or “programmed”) to any combination you want. It’s like your suitcase or attache case. Except it doesn’t use wheels. It uses switches, not unlike the light switches in your home.

These switches (”dip switches”) are very tiny and there may be as many as ten of them under the cover of the opener.

(click the picture on the left for a larger view)

Not only that — there are ten under the cover of each remote control. So your opener and the accompanying remotes are a matched set — programmed at the factory to have the identical combination. You can change the combination any time you want by programming the remote controls and the base unit to the same combination.

But how many possible combinations are there? It turns out there are 1,024 different combinations.

How do you figure that?

Well, start with the idea that a switch can only be set to two different positions: “on” or “off.”

So, if you have ten switches here are just three of the many combinations you could have:

off-off-off-off-off-off-off-off-off-ON, or
off-off-off-off-off-off-off-off-ON-ON, or
off-ON-off-ON-off-ON-off-ON-off-ON and so on…

Here’s what this has to do with Internet addressing:

If we pretend that every house has a “10-switch” garage door opener, then we can say that there are 1,024 different combinations that we can dole out to the houses in a neighborhood.

In other words, each house has a unique address that is the same as the combination of their garage door opener.

Your computer, in turn, has a unique address on the Internet and it uses the same idea — bits that are set to provide a combination.

But on the Internet we need more combinations, or addresses than can be provided by a 10-switch (or “10-bit”) addressing system.

So we use a “32-bit” addressing system. And that gives us enough possible combinations to provide nearly enough addresses for every man, woman and child on Earth.

More on this in another post.

Here's A Few More Related Posts:
  1. How does a computer count to 1,024?
  2. What is your computer’s address?
  3. How to make sense out of IP addressing
  4. My computers can’t understand each other

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