metric : Java Glossary

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©1996-2017 Roedy Green of Canadian Mind Products

metric

aka Système Internationale is a decimal system of measures used nearly everywhere but in the USA. Even in the USA, it is used in medicine, scientific and engineering work and for international trade.

You might wonder why the USA alone sticks with the old complicated Imperial system of measure. The Christian right lobby in the USA hates metric because it was invented by atheists and the worst kind, French during the French revolution.

It is based on standard prefixes. e.g gram (the mass of about a sugar cube of water), kilogram (a 100 grams), milligram (one thousandth of a gram) or metre (a little longer than a yardstick), kilometre (1000 metres, about 5/8 mile), millimetre (one thousandth of a metre). I use both forms of measure on this website, since there are so many American visitors.

Because RAM (Random Access Memory) necessarily comes in modules sizes of even powers of two, the prefix scheme was modified for measuring bytes by even powers of two. Unfortunately, vendors use the binary scheme for measuring RAM capacity but the decimal scheme for measuring hard disk capacity. I suspect they do this primarily to inflate the apparent disk capacity by 7% and because their competitors also do this, rather than as protest against the heretic binary RAM byte measuring prefix convention.

Metric/Imperial Equivalents

Metric Equivalents
Unit Metric Imperial
milligram1 mg0.02 gr
gram1 gram15.43 gr
kilogram1 kg2.20 lbs
millimeter (millimetre)1 mm0.04 in
centimeter(centimetre)1 cm0.39 in
meter (metre)1 metre3.28 ft
kilometer (kilometre)1 km0.62 mile
milliliter (millilitre)1 ml0.20 US teaspoon
litre (litre)1 litre1.06 US quarts
meter/sec (metre/sec)3.60 km/hr2.24 mph

In Canada, the English and French spellings are used interchangeably. The French invented metric, so the French spelling has extra cachet.

You can improve your metric weight intuition by asking the post office to weigh a few objects for you.

SI (Systèm Internationale (metric)) Prefix Summary

SI prefixes
Factor Name  Symbol
1024 yotta Y
1021 zetta Z
1018 exa E
1015 peta P
1012 tera T
109 giga G
106 mega M
103 kilo k
102 hecto h
101 deka da
  
Factor Name  Symbol
10-1 deci d
10-2 centi c
10-3 milli m
10-6 micro µ
10-9 nano n
10-12 pico p
10-15 femto f
10-18 atto a
10-21 zepto z
10-24 yocto y

SI Prefixes

prefix American English Standard Decimal
Multiplier		 Power of 10 Byte Measure
Multiplier		 Byte Measure
Power of 2
exa quintillion
(British trillion)		 1,000,000,000,000,000,000 1018 1,152,921,504,606,846,976 260
peta quadrillion 1,000,000,000,000,000 1015 1,125,899,906,842,624 250
tera trillion
(British billion)		 1,000,000,000,000 1012 1,099,511,627,776 240
giga billion 1,000,000,000 109 1,073,741,824 230
mega million 1,000,000 106 1,048,576 220
kilo thousand 1000 103 1024 210
hecto hundred 100 102    
deca ten 10 101    
deci tenth 1/10 10-1    
centi hundredth 1/100 10-2    
milli thousandth 1/1000 10-3    
micro millionth 1/1,000,000 10-6    
nano billionth 1/1,000,000,000 10-9    
pico trillionth
(British billionth)		 1/1,000,000,000,000 10-12    
femto quadrillionth 1/1,000,000,000,000,000 10-15    
atto quintillionth
(British trillionth)		 1/1,000,000,000,000,000,000 10-18    

There are a series of Greek, Latin, Danish and Spanish prefixes used for specifying large numbers. The prefixes have different meaning when talking about RAM than when talking about disk space.

Two Kinds of Gigabytes

Hard disk capacities are measured in decimal gigabytes, in billions of bytes, namely 109 = 1000x1000x1000 = 1,000,000,000 bytes.
106 means 1 followed by 6 zeros, i.e. 1,000,000.
10-6 means 1 in the 6th decimal place, i.e. .000001.

However, Windows measures hard disk capacity using the binary RAM definition.

For measuring RAM, a gigabyte is a little over a billion bytes, or more precisely, 1024 megabytes = 230 bytes = 1024x1024x1024 bytes = 1,073,741,824 bytes. A byte is approximately one character of information.

Two Kinds of Megabytes

A megabyte on disk is precisely a million, namely 109 =1000x1000x1000 = 1,000,000 bytes. For RAM it is a little over a million bytes, namely 220 = 1024 × 1024 = 1,048,576 bytes.

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