Currently, according to mainstream media, bandwidth is defined as the quantity of data you download or upload to the internet over a month. So, for example, your ISP will tell you the maximum bandwidth limit is 100GB. Or whatever.

That, however, is not it’s true definition. It’s true definition is:
a data transmission rate; the maximum amount of information (bits/second) that can be transmitted along a channel ¹

This is the secret thing about bandwidth. ISPs don’t care about how much you upload to the web over a given period. We care about how fast you upload it.

When you pay for a high-level connection to the internet, that you use to connect houses to, or web-serving computers, you do not pay in quantity over time. You pay in speed. So, for example, 1 gigabit per second. If you go over that speed, longer than a allowed ‘burst’ period, you pay an overage charge, always assuming that your network is even capable of going over that speed.

Think of bandwidth like gas going through a pipe. (Terrible, terrible analogy, I know. But it’s the easiest way to explain.) That gas can only flow so fast, and only so much can be fit in the pipe at any one time. We don’t particularly care if you use 100GB by taking a trickle out of the system at any one time. We do care if you take a torrent.

Realistically though, customers never notice bandwidth. They’re too busy playing with computer-resource hungry things, like wordpress, to even be able to consume all of their allocated bandwidth. Only very, very rarely do we actually start thinking about bandwidth rather than computing resources. Normally, it’s podcasts. Static file. Almost no server-resources required to send it out onto the internet. But it eats bandwidth. Most are ~50-80Megabytes per episode. You get enough people downloading that simultaneously, and we’re going to start noticing…

As long as the current trend continues, i.e. the more computing power we have available to provide you with your shiny websites, the more the people creating the shiny websites waste computing power, the mainstream will never notice this secret.

More often than not, the reason we ask people to upgrade off our shared servers, is not because they’ve reached any arbitrary bandwidth limit, although we may use this as a guide to identify them. It’s because they’re using too much CPU time.