What is the difference between bandwidth and download speed?
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The bandwidth is the maximum amount of data that can travel over the connection. This will normally be constant but for some connection types can vary. It an also sometimes be shared e.g. your internet bandwidth is shared between all the things in your house that want to talk to the outside world.
The download speed is how fast a file is arriving at your computer. This will always be less than the bandwidth due to overheads (see below) but could be significantly lower since it will be limited by the slowest part of the connection between you and the place you are downloading from.
Overhead is all the other stuff going on over a network connection that you don’t care about, a lot of it is invisible to the user. During a download there will requests for the next block, acknowledgements that messages have arrived etc… There will normally also be a small amount of housekeeping data maintaining the link. Wireless links often have a lot more overhead since they require more constant status checking than a wire.
While this is generally a small amount of data it does reduce the maximum rate available for the actual thing you are downloading.
And there will be gaps in data while the computer at the other end works out what to send next. Although these aren’t technically overhead the need for some processing time means it’s rare to hit 100% on a link for long periods.
Edit-just to note in advertising the two will often be used interchangeably, maximum download speed and bandwidth are normally close enough to not make much difference.
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