Back to Part One.

In terms of computing, metric prefixes have been tricky to use, since computers work in terms of powers of two, rather than powers of ten. New binary prefixes were invented a few decades ago. They match the metric prefixes in every respect except two: the shorthand symbols are slightly different, and, of course, the numerical values. Contrary to the name's suggestion, these binary prefixes are used with decimal numbers; just not the powers of ten we are used to. They can also be used with binary numbers anyway. Confused? So am I.

## A list of some more common and less common binary prefixes

```Power of 2	Name	Numerical Equivalent
0		-----	1 (one)
10		Kilo	1,024 (one thousand and twenty-four)
20		Mega	1,048,576 (one million, forty-eight thousand, five hundred and seventy-six)
30		Giga	1,073,741,824 (one billion, seventy-three million, seven hundred and forty-one thousand,
eight hundred and twenty-four)
40		Tera	1,099,511,627,776 (one trillion, ninety-nine billion, five hundred and eleven million,
six hundred and twenty-seven thousand, seven hundred and seventy-six)
50              Peta    1,125,899,906,842,624 (one quadrillion, one hundred and twenty-five trillion,
eight hundred and ninety-nine billion, nine hundred and six million, eight hundred and forty-two thousand,
six hundred and twenty-four)
```
A list of higher prefixes is available on Wikipedia.

Why are there no prefixes for negative powers of two? In computers, where this system is used the most, there is no unit smaller than a bit, eight of which make one byte, which is the fundamental unit of memory and storage.

For those people looking for the shorthand symbols, here they are, including those of higher prefixes, and their alternative (and preferred by the IEC):

```Yotta   Yobi	Yi
Zetta   Zebi	Zi
Exa     Exbi	Ei
Peta    Pebi	Pi
Tera    Tebi	Ti
Giga    Gibi	Gi
Mega    Mebi	Mi
Kilo    Kibi	ki
```

## The Difference between a KB and a KiB

A KB (kilobyte) is one thousand bytes. A KiB (kibibyte) is one thousand and twenty-four bytes. Easy, huh? Conversion into bits is also easy: just multiply whatever you have by 8. A kilobyte is eight thousand bits, a kibibyte is eight thousand, one hundred and ninety-two bits. It's the same for everything else. (Except, of course, the numbers themselves.)

Why are these binary prefixes so important? The percentage difference between a KB and a KiB is ±2.4% either way. However, when prefixes as low as peta are used, the percentage difference is over ±20%. As disk storage gets larger and larger, these differences need to be sorted out. Thankfully, these prefixes are being used more often worldwide.