# What is Bandwidth? - Usage, Limits & Measurement

Instructor: Lonny Meinecke

Lonny teaches psychology classes at King University, and has a bachelor's degree in IT and a doctorate in psychology.

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.

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