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Bits and Bytes

Nothing to do with web development, but a topic that seems to be widely misunderstood relating to Internet connection speed …

Question:

  • My server provider, Talk Talk, advertise ‘Up to 8 Meg download speeds’. What does this actually mean?

Answer:

  • By 8Meg, they are in fact referring to 8Mbps (megabits per second), not MBps (megabytes per second). This can be misleading since people often quantify the amount of data they are downloading in megabytes (MB). So if, for example, you were to download a 10MB file, over this 8Mbps Internet connection, it would in theory take 10 seconds. I say in theory, because few people ever hit their advertised speed – factors such as distance from the exchange, congestion and traffic shaping can all slow down the connection speed.

To Explain The Above:

As the names imply, megabit refers to individual bits, whilst megabyte refers to a unit of 8 bits. Most authors use the convention whereby: Mbps = megabits per second & MBps = megabytes per second. The conversion is easy: 1 byte equals 8 bits, so 1 MBps = 8 Mbps.

Most networking hardware is rated in megabits per second. For example, a 10Base-T Ethernet operates at 10 megabits per second and a 100Base-T Ethernet operates at 100 megabits per second. Internet access is also measured in megabits per second. Although service providers seem to do their very best to confuse the issue by often quoting their speeds in Meg.

So in the Talk Talk example above, where a 10MB file is being downloaded over an 8Mbps Internet connection – the calculation is as follows:

  • 10MB (megabytes) = 80Mb (megabits) – remember 8 bits in a byte.
  • 80Mb (megabits) / 8Mbps (megabits per second) Internet speed = 10 seconds.