Mibi Mega Kibi Kilo — Decimal and Binary Prefixes

A mega­bit can be 1,000,000 bits or 1,048,576 bits depend­ing on whether you using decimal or bin­ary defin­i­tions. Standards have been defined to help — are you using the mib­i­b­yte and kib­i­b­yte in your documentation ?

The dif­fer­ence between bin­ary and decimal seems small, but it can lead to very large prob­lems. Instances of tel­cos provid­ing band­width in decimal can cause QoS strategies to go wrong as this makes a big dif­fer­ence when traffic shap­ing. Or when cal­cu­lat­ing file trans­fer times for large files, you can intro­duce a large mar­gin for error.

Standards for decimal and bin­ary prefixes

In 1999, the International Electrotechnical Commission (IEC) pub­lished a stand­ard, which was approved in 1998, intro­duced the pre­fixes kibi–, mebi–, gibi–, tebi–, pebi–, exbi–, to be used in spe­cify­ing bin­ary mul­tiples of a quant­ity. The names come from the first two let­ters of the ori­ginal SI pre­fixes fol­lowed by bi which is short for “bin­ary”. It also cla­ri­fies that, from the point of view of the IEC, the SI pre­fixes only have their base-​​10 mean­ing and never have a base-​​2 meaning.

Thus kibi is a kilobyte in binary — kibi and a gibibit is a bin­ary gigabit.

IEC stand­ard prefixes

In 1999, the International Electrotechnical Commission (IEC) pub­lished Amendment 2 to “IEC 60027 – 2: Letter sym­bols to be used in elec­trical tech­no­logy – Part 2: Telecommunications and elec­tron­ics”. This stand­ard, which was approved in 1998, intro­duced the pre­fixes kibi–, mebi–, gibi–, tebi–, pebi–, exbi–, to be used in spe­cify­ing bin­ary mul­tiples of a quant­ity. The names come from the first two let­ters of the ori­ginal SI pre­fixes fol­lowed by bi which is short for “bin­ary”. It also cla­ri­fies that, from the point of view of the IEC, the SI pre­fixes only have their base-​​10 mean­ing and never have a base-​​2 mean­ing. It is strongly sup­por­ted by many stand­ard­iz­a­tion bod­ies, includ­ing IEEE and CIPM.

Examples

Example: 300 Gigabytes = 279.5 Gibibytes.

Decimal pre­fixes

Why bother ?

When you are traffic shap­ing a 128kbps cir­cuit, is it 128000 bits per second or is it 131072 bits per second ?

When you buy a 10 mega­byte per second Internet con­nec­tion, is it 10,000,000 bits per second or 10,485,760 ? That is quite a big dif­fer­ence isn’t it ?

By get­ting people to use these abbre­vi­ations, we should get this more cor­rect in the future. To show how the error factor can creep into net­work plan­ning, have a look at the per­cent­age dif­fer­ence table below:

Approximate ratios between bin­ary pre­fixes and their decimal equivalent

Conclusion

I would like to hear what other people think ? Could this be done ? Would you do this it at work ? Or am I full of hot air ?

And for what’s is worth, this is ter­min­o­logy that I use more and more often. It’s a lot more accur­ate when cal­cu­lat­ing QoS and file trans­fer times.

Reference

Wikipedia HERE

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