In this lesson, we’ll go over what bandwidth is in relation to computers and digital gadgets.

We’ll also talk about bandwidth usage, bandwidth limits, and how bandwidth is measured.

## What is Bandwidth?

Bandwidth is about throughput. In networks, **bandwidth** refers to how much digital information we can send or receive across a connection in a certain amount of time. Sometimes it’s called **data transfer rate** too.Most of the time, bandwidth refers to maximum throughput, and the information that is sent through is expressed in bits per second (a bit is the smallest unit of digital data that is represented as a 1 or 0). Since the number of bits can be a really large number, we might use a term like kilobits per second (Kbps or 1,000 bits per second) or megabits per second (Mbps or 1,000,000 bits per second) for how many bits can be sent or received in a second. An example of a common internet speed is around 10Mbps (megabits per second), which works out to about 1.

3MBps (megabytes per second). That’s pretty fast!By the way, if you’re wondering how 10Mbps works out to approximately 1.3MBps, simply divide by 8, which is the number of bits in each byte.Bear in mind that this kind of bandwidth is used to describe networking.

Bandwidth can also refer to processor bandwidth, which is measured in hertz. So, if you might sometimes feel confused, just remember that network bandwidth usually refers to maximum bits per second.

## A Metaphor for Bandwidth

Maybe it would help if we used a familiar example to help visualize what bandwidth means. Long ago, ships used to use signal lamps (also called Aldis lamps) to communicate across the water. The signal lamps could be on or off (1 or 0), a lot like how bits in computers can be on or off. By opening and closing a kind of shutter, bits of information (flashes of light) could be exchanged (similar to 1s and 0s). The maximum amount of these flashes of light that could be sent was about 14 wpm (14 words per minute), which works out to 5 bits per second, more or less.

So you see, 5 bits per second was the **bandwidth** of an Aldis lamp (with a really good operator!). Now compare that to bandwidth today, with speeds like 1 million or more ‘flashes’ per second. If that were a signalman, he or she would get awfully tired!

## Bandwidth Limits and Issues

A good way to think of **bandwidth limits** is by thinking of an internet connection like a water hose, and the limits in terms of the rates of water that you can get in a fixed amount of time. The physical hose is only so big, the amount of water is limited, and service providers might limit you by the hour, day, and/or month. You may be allowed 10 gallons per hour, for example, and 100 gallons per day. If you go over that, your provider may shut off your water supply.

Digital bandwidth from many internet service providers (ISPs) is a lot like that. A bigger issue, though, is how your throughput can get congested, and limit the speed of your network connection. If you’re the only one in your house streaming videos, your network bandwidth probably won’t be as congested as you streaming videos while a family member video conferences with someone overseas and other folks in your house are playing online video games. All those network intensive activities add up and limit your overall throughput and speed.

## Bandwidth Usage

So far, we’ve been talking about maximum throughput. You may end up using part or all of your maximum throughput. That’s your usage. Say you don’t download much of anything one month, and the next month a great video comes out so you do a lot of downloading of that movie. Each time you transfer data, that’s part of your total **bandwidth usage**.

## How is Bandwidth Measured?

We’ve actually kind of covered this, but let’s do an example.

Bandwidth is measured by the data transfer rate, and by your total usage. You can only use so much at a time (right away), and you can only use so much per month total. If you download a 20MB file, you’ve used 20MB of bandwidth. If you download it again to show someone else, now you’ve used 40MB total. If your limit is 50MB, you won’t have much left.However, all of these figures (bits per second, total limits or usage per month) are kind of hard to calculate because there are so many factors to consider. Some of these issues include how many connections you have, everything that is running at the time, the geographic distance between you and the other end of the connection (like the location server hosting the website that you’re visiting), and other fluctuations.

It may be simpler to just experiment a little and see which data plan meets your needs, rather than trying to calculate it.

## Lesson Summary

Bandwidth describes network throughput: it refers to how much digital information we can send or receive across a connection in a certain amount of time. A good way to think of bandwidth limits is by thinking of an internet connection like a water hose, and the limits in terms of how much water is you get in a fixed amount of time. Each time you transfer data, that’s part of your total bandwidth usage. Bandwidth is measured by the data transfer rate, and by your total usage.

You can only use so much at a time (right away), and you can only use so much per month total. By measuring bandwidth, we can help calculate how much we’re going to need, and how much we’ve used, so users get what they need, when they need it, so that the billing can be accurate. So when you think about bandwidth, think about throughput, Aldis lamps, and water hoses.