Where Did Kilo, Mega, Giga Come From..?

They have entered our language. Everyone uses them. The terms, particularly with "byte", are almost commonplace. By convention multiples greater than one should be specified with a capital letter and those less that one with a lower case. Thus "Km" is correct but "km" is not.

The terms and their mathematical values are: (for those that "tend to infinity")

Deca   10^1 10 Greek meaning ten.
Hecta   10^2 100 Greek meaning hundred.
Kilo 1000^1 10^3 1,000 From Greek khiloi meaning 1000.
Mega 1000^2 10^6 1,000,000 From the Greek mega meaning "great", as in Alexandros Megos (Alexander the Great).
Giga 1000^3 10^9 1,000,000,000 From Latin gigas meaning "giant". Generally accepted as the value called a "Standard billion" in preference to the "English Billion which is only one hundred million.
Tera 1000^4 10^12 1,000,000,000,000 A "Standard Trillion". From Greek teras meaning "monster".
Peta 1000^5 10^15 1,000,000,000,000,000  From Greek pente meaning five (for 1000^5 = 1000 raised to the power five). This term and the next were added in 1975 by the General Conference of Weights and Measures (CGMP).
Exa 1000^6 10^18 1,000,000,000,000,000,000 From Greek hex meaning six. Taking "Hexa" and making the "H" silent (France is the home of  the CGMP) gives "Exa".
Zetta 1000^7 10^21 1,000,000,000,000,000,000,000 Not to be mistaken for Greek Zeta. Last letter of the Latin alphabet. This prefix and the next were added in 1990 by CGMP.
Yotta 1000^8 10^24 1,000,000,000,000,000,000,000,000 Penultimate letter of the Latin alphabet.
Bronto    1000^9 10^27 1,000,000,000,000,000,000,000,000,000 Just keep on getting bigger... From the greek for Thunder.

And going in the other direction, we have the terminology and amounts for numbers that "tend to zero" less than 1 (unity) but never truly reaching 0 - although the amounts can be so tiny that they can mostly be considered zero for all but scientific reasons. Note the terms less than 1 are written with a lower case letter. So you might have 1Mb but it takes 20mSec to fill it. Because there is repetition in some of the letters, micro is represented by the Greek letter "μ" (mu, pronounced 'myoo') similar-looking and often written as English "u".

deci 10^-1 0.1 One tenth part, 1/10.
centi 10^-2 0.01 One hunderdth part, 1/100.
milli 10^-3 0.001 One thousandth part, 1/1000.
micro 10^-6 0.000,001 One millionth part, 1/1,000,000.
nano 10^-9 0.000,000,001 One thousandth millionth (one standard billionth), 1/1,000,000,000.
pico 10^-12 0.000,000,000,001 One million, millionth part, 1/1,000,000,000,000.
femto 10^-15 0.000,000,000,000,001 One million billionth part, 1/1000,000,000,000,000.
atto 10^-18 0.000,000,000,000,000,001 One billion billionth part, 1/1000,000,000,000,000,000.
zepto 10^-21 0.000,000,000,000,000,000,001 One thousand billion billionth part, 1/1000,000,000,000,000,000,000.
yocto 10^-24 0.000,000,000,000,000,000,000,001 One million billion billionth part, 1/1000,000,000,000,000,000,000,000.

Some find it useful to view a direct comparison of the above - it provides perspective on the scales...

 Approaching Infinity <--------------|--------------> Approaching Zero

                                    0.000,000,000,000,000,000,000,001  yocto  10^-24
                                    0.000,000,000,000,000,000,001      zepto  10^-21
                                    0.000,000,000,000,000,001          atto   10^-18
                                    0.000,000,000,000,001              femto  10^-15
                                    0.000,000,000,001                  pico   10^-12
                                    0.000,000,001                      nano   10^-9
                                    0.000,001                          micro  10^-6
                                    0.001                              milli  10^-3
                                    0.01                               centi  10^-2
                                    0.1                                deci   10^-1
                                    1                                  Unity  10^0
                                   10                                  Deca   10^1
                                  100                                  Hecta  10^2
                                1,000                                  Kilo   10^3
                            1,000,000                                  Mega   10^6
                        1,000,000,000                                  Giga   10^9
                    1,000,000,000,000                                  Tera   10^12
                1,000,000,000,000,000                                  Peta   10^15
            1,000,000,000,000,000,000                                  Exa    10^18
        1,000,000,000,000,000,000,000                                  Zetta  10^21
    1,000,000,000,000,000,000,000,000                                  Yotta  10^24
1,000,000,000,000,000,000,000,000,000                                  Bronto 10^27

Many of the above grouping terms are bandied about with little regard to the sheer size of the number. Consider the following:

There are 86,400 seconds in one day. Assuming an average life span of 80 years, each of us has 2,522,880,000 seconds to live. Sounds quite a lot, but consider this: If you are middle-aged, you have around a billion seconds left to live. Can you hear ticking?

But what is that Billion in comparison?

  • A billion seconds ago Britain was wracked with the poll-tax riots and unemployment was at an all time high in the "loads-a-money" era.
  • A billion minutes ago Jesus was alive.
  • A billion hours ago our ancestors had only just learned to use rocks to manipulate their environment and their global population numbered, probably, just a few thousand.
  • A billion days ago no mammal walked on two feet.
  • A billion years ago multi-cellular, complex animals had recently formed from single-cell creatures. Around half as much time again would pass before recognisable animals evolved.
  • A billion decades ago there was no Sun or Earth. This region of our galaxy was populated by super-giant stars that lived short lives (~500 million years) and died incredibly violent deaths to seed a vast dust cloud that would eventually become the Solar system including all the planets and You.
  • Two billion decades ago there was nothing. The entire universe was probably an (almost) infinitely hot, infinitely dense, infinitely small dot and even the numbers mentioned here can only approximate those required to model it with today's super computers.
  • But... Two billion Pounds ago was only 26 hours and 24 minutes, at the rate our government is spending it.

hmmm. >:o/