What is Bandwidth?

The Internet consists of tens of millions of computers throughout the world, all connected by cables. Your ISP (Internet Service Provider) is a company that has a very high-speed (and very expensive) connection to the Internet. Your ISP makes its money by renting little "chunks" of that high-speed connection to consumers who don't want to spend thousands of dollars each month for an Internet connection.

If you've ever wondered why it takes so long to download certain Web pages or other files to your computer, it's all determined by the bandwidth of the connection between your computer and your Internet Service Provider. Which is to say, it all hinges on that wire connecting your computer to your modem to your ISP. That connection is often referred to as the last mile, as illustrated in Figure 1.

When you open a Web page or download a file, it travels very quickly from wherever it happens to be on the planet Earth to your ISP. It then travels from the ISP's computers to your computer. The actual speed at which information moves through a wire is always the same, no matter what your bandwidth might be. That is, electrons run through the wires at close to the speed of light, about  670,000,000 MPH (six hundred and seventy million miles per hour). At that speed, you could circle the globe 7 times a second, or 420 times a minute. So why does it take so long for every Web page you visit to appear on your screen? That's where bandwidth comes in.

Bandwidth is easy to understand if we use an analogy from everyday life. Imagine that instead of trying to get a Web page or file from your ISP through wires, you're trying to drain a swimming pool. The water in the pool is the Web page or file. If you stick a skinny hose to drain the water from the pool, as in Figure 2, it will take quite a while to drain all the water.

Figure 2

Now let's say that instead of sticking a skinny pipe onto the pool we put on a big fat pipe, as in Figure 3. I donít think it takes a physics major to realize that itís going to take less time to drain the pool in Figure 3 than it is to drain the pool in Figure 2.

 

Figure 3

We can say that the fat drain pipe in Figure 3 is "wider" than the pipe in Figure 2. Or, we could take it another step and say that the fat pipe in Figure 3 has more bandwidth than the skinny pipe. And ultimately, that's what bandwidth is all about. How much stuff can pass through the pipe (or wire) at a time.

Dial-up Internet accounts, which use a standard telephone line to connect to an ISP, have a very narrow bandwidth (about 50 Kbps or 50,000 bits per second). Thus, things are slow in the sense that it takes a long time to download things.

A broadband Internet account can move data at anywhere from 128 Kbps to 2,000 Kbps or more. That's like the fat drain pipe. It takes a lot less time to get a Web page or file from your ISP's computer to your computer using the broadband account than it does the dial-up account.

So the whole bandwidth thing (like many things "computerish") boils down to a time vs. money decision. You can either spend the extra amount per month for a faster connection, and spend less time waiting for things to download. Or, you spend less money on a dial-up account, but spend more time waiting for things to appear on your screen.

Alan Simpson


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