Tutorials & help

Computer units

Summary

• bs and Bs
• Decimals multiples
• Binary multiples
• Examples
• Finally...

bs and Bs

b stands for bit. It's a binary digit : 0 or 1.
B stands for byte. It's composed of 8 bits. So a byte can take 256 values, from 0 (00000000) to 255 (11111111).

Decimals multiples

You surely know most of them :

Factor	Prefix	Symbol
103	kilo	k (or K)
106	mega	M
109	giga	G
1012	tera	T
1015	peta	P
1018	exa	E
1021	zetta	Z
1024	yotta	Y

Binary multiples

At the beginning, computer professionals were using the binary multiple values associated with decimal multiple names, because they noticed that 1,024 (=2¹⁰) was close to 1,000 (=10³), and as they were using the binary system, binary multiples were more practical for them.
Eg, 1 kilobyte meant 1,024 bytes.
But then, more and more "common people" bought computers, and these new users most often knew that one kilo means 1,000, so it became quite confusing : we had two unit systems but both had the same names.
Now, 1 kilobyte should be 1,000 bytes, and 1,024 bytes should be 1 kibibytes. This system was adopted on december 1998 by the International Electrotechnical Commission (IEC).
Binary multiple names are constructed as follow : beginning of the decimal prefix + "bi". Eg, kilo → kibi.
Binary multiple prefixes are contructed by adding "i" after the decimal multiple. Eg, M → Mi.

Factor	Origin	Prefix	Symbol
210	kilobinary	kibi	Ki
220	megabinary	mebi	Mi
230	gigabinary	gibi	Gi
240	terabinary	tebi	Ti
250	petabinary	pebi	Pi
260	exabinary	exbi	Ei
270	zettabinary	zebi	Zi
280	yottabinary	yobi	Yi

Pronunciation : first syllable like the decimal prefix, "bi" like "bee".

Examples

1 KiB = 1.024 KB = 1,024 B
1 KB = 1,000 B = 0.9765625 KiB
1 GiB = 1,024 MiB = 1,048,576 KiB = 1,073,741,824 B
1 GB = 1,000 MB = 1,000,000 KB = 1,000,000,000 B = 0.931322574615478515625 GiB

Finally...

We'll apply the new units to all our pages created after today, and migrate progressively the others.
This short tutorial was created using the following sources :

• Definitions of the SI units: The binary prefixes
• Binary

For more informations, see these sources.