Bits and Bytes

By Simon Kewin

In its election manifesto, one of the major political parties in the UK recently promised to provide “virtually every household in the country a broadband service of at least 2 megabytes per second by 2012.”

The “2 megabytes per second” was actually a mistake. A speed of two megabytes per second is the same way as saying 16 megabits per second, a speed which is technically feasible, but unlikely to be universally available in the UK any time soon. The sentence was altered in later versions of the manifesto to the much more realistic “2 megabits per second”. The typo, however, highlights how easy it is to make mistakes using technical language where words often have very specific meanings. If you’re using terminology from medicine, computers, statistics etc., it pays to check that you have each term correct.

In this case, the original authors confused the words bit and byte. Both are units of computer memory/storage. A bit is the smallest amount of storage, a 0 or a 1, the word formed from a blend of “binary” and “digit”. A byte, on the other hand, is a collection of bits – almost always eight of them. So, a kilobyte is eight times larger than a kilobit.

While computer memory is generally expressed as a number of bytes (kilobytes, megabytes, gigabytes etc.), network speeds are generally expressed as a number of bits per second (kilobits, megabits, gigabits etc.) The terms are very easy to confuse especially when they are abbreviated to just “meg”, “gig” etc. as both sets sometimes are. But, a broadband speed of “2 meg” would always mean “2 megabits per second” and never “2 megabytes per second”.

Abbreviations are often used for these terms, and the same care needs to be taken. For example, the abbreviation for megabyte is MB whereas the abbreviation for megabit is Mb. The case of the “b” makes all the difference. The same is true for kilobytes/kilobits (KB/Kb), gigabytes/gigabits (GB/Gb) and so forth.

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5 Responses to “Bits and Bytes”

  • Brad K.

    In it’s original incarnation, for teletype text speed descriptions (where the great leap from 110 baud to 300 baud was really big news), it was generally accepted that the parity and control bits added to each 7 or 8 bit transcription of text characters were counted in the transmission of data.

    In general, the control words and bits came to about 10 total bits, 7 or 8 bits to represent the character, and 2 to 3 bits, on average per transmission of a string of text, for parity (quality check) and control (start, stop, identification, accept or reject control words). Thus, the baud rate, which is today called bit rate, has been generally accepted to be 10 bits per character, and is now considered 10 bits per 8 bit byte of data.

    So to convey 2 megabytes of data, I would look to 18-20 megabits per second of actual transmission rating and throughput.

    The flip side of 2 megabytes per second is the telecom multiplexing strategy. That is, serve 100 homes or accounts with a shared 100 megabit per second “trunk” line. That 100 mps line would equate to 10 megabytes of data, and if on average, only 5 of those homes are using their total 2 megabytes per second “full speed” loading rate – then the 100 homes are served with 2 megabytes per second bandwidth. This lets the telecom play a numbers game, and ignore the degraded service while 90 of the 100 homes are trying to watch the same video – or the same football match.

    In this case, I would be interested to know if the quote came from a telecom marketing type or a lobbied politician, or a technical specification. The technical details would likely express the technical terms in bits or megabits per second, while the shills and marketers would quote much-massaged rosy picture numbers.

    But I am guessing, not knowing the background and details of the proposal.

  • Simon Kewin

    Brad,

    Thanks for the input. The quotation was from the election manifesto of the UK Labour Party. It was a clear mistake and they corrected it in subsequent versions. I think they were using technical terms without really understanding them.

    Simon.

  • Jered

    I wonder how many techies jumped up and down at the announcement, only to realize later that the wording was a mistake?

    This is an excellent case study in how one tiny mistake could potentially cost a person or organization big time.

    Thank you for researching and sharing this information, Simon.

  • Peter

    Strictly speaking, baud rate and bit rate are not the same thing. The baud rate is the number of changes in the transmitted signal per second, and on an analog telephone line, each tone can encode many bits.

  • Simon Kewin

    Peter,

    Absolutely! I recall being taught all about “bits per baud” many years ago …

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