Click here to purchase the entire book in PDF format.

Prefixes

Similarly, prefixes make our lives much easier by acting as built-in multipliers in our spoken numbers. It's too difficult to talk about very short distances in meters - so we use millimeters. A large resistance is more easily expressed in k$\Omega$ than $\Omega$.

Table 1.6: Prefixes with corresponding multipliers, both for the real world and for computer people.

Prefix	Abbrev.	Normal	Computer
		Multiplier	Multiplier
atto-	a	$10^{-18}$
femto-	f	$10^{-15}$
pico-	p	$10^{-12}$
nano-	n	$10^{-9}$
micro-	$\mu$	$10^{-6}$
milli-	m	$10^{-3}$
centi-	c	$10^{-2}$
deci-	d	$10^{-1}$
		1	1
deca-	da	$10^{1}$
hecto-	h	$10^{2}$
kilo-	k	$10^{3}$	$2^{10}$
mega-	M	$10^{6}$	$2^{20}$
giga-	G	$10^{9}$	$2^{30}$
tera-	T	$10^{12}$	$2^{40}$
peta-	P	$10^{15}$	$2^{50}$

So, for example, if you see something written in kilometers (abbreviated km), then you know that you must multiply the number you see by $10^{3}$ to convert to metres. 5 km = 5 * $10^{3}$ m = 5,000 m. If the unit is milligrams (mg), then you multiply by $10^{-3}$ to convert to grams (g). 15 mg = 15 * $10^{-3}$ g = 0.015 g.

If you're dealing with computer memory, however, you use the other column in Table 1.6. A computer with 20 Gigabytes (GB) of hard disk space has 20 * $2^{30}$ bytes = 21,474,836,480 bytes.

Note that, if the prefix denotes a multiplier that is less than 1, it starts with a small letter (i.e. milli- or m). If the multiplier is greater than one, then a capital letter is used (i.e. mega- and M). The odd exception to this case is that of kilo- or k. I don't know why this is different, I guess somebody has to be...