A mega byte is approximately 1 Million bytes of information. The prefix
indicates how large the number is. The prefixes most commonly used
originate from the metric system's powers of 10. Most people are familiar
with these prefixes is use with measurements of distance (meter, millimeter,
kilometer etc...). Each of these prefixes describes the power to which you
raise 10. For instance a kilometer indicates that 10 is raised to the 3rd
power or 10^{3}=1000. Therefore 6 kilometers is 6x10^{3}=6000
meters. The following chart indicates the metric prefix, the appropriate
power of 10 and the decimal equivalent:
Prefix 
Power of 10^{x} 
Abbreviation 
Decimal Equivalent 
exa 
10^{18} 
E 
1,000,000,000,000,000,000 
peta 
10^{15} 
P 
1,000,000,000,000,000 
tera 
10^{12} 
T 
1,000,000,000,000 
giga 
10^{9} 
G 
1,000,000,000 
mega 
10^{6} 
M 
1,000,000 
kilo 
10^{3} 
k 
1,000 
centi 
10^{2} 
c 
.01 
milli 
10^{3} 
m 
.001 
micro 
10^{6} 
m 
.000001 
nano 
10^{9} 
n 
.000000001 
pico 
10^{12} 
p 
.000000000001 
fempto 
10^{15} 
f 
.000000000000001 
atto 
10^{18} 
a 
.000000000000000001 
When it comes to digital files things are a little different. I say
approximately 1 million bytes because of the way digital information is
defined. Digital files that the computer interprets are written in
binary. Which means that each bit (Binary Digit) of information has 2^{1}=2
possible values, 1 or 0. Therefore, each bit can describe something in one
of two ways either on (1) or off (0). So in order to get higher levels of
description other than on or off, extra bits are added in a string. Once 8
bits are combined in a string they are called a byte. A byte is comprised
of 8 bits and can therefore describe something in 2^{8}=256 ways.
One byte is the quantity of information required to describe one computer
character such as the letter "K". A 24 bit file indicates that
something can be described 2^{24}=1,677,216 ways. This is
why you see 24bit color sometimes described as millions of colors. So,
back to the Megabyte, in binary terms a Megabyte (Mb) is actually 2^{20}=1,048,576
bytes, not 1,000,000 bytes as would be suggested by the metric prefix and a
Gigabyte (Gb) is actually 2^{30}=1,073,741,824 bytes not
1,000,000,000. This holds true for most digital storage and virtual memory
values, but there is some cross usage of the terms for different storage devices
and by different manufacturers, so you may not know exactly how many bytes any
given device has in a Megabyte. However, almost all other uses of the prefixes are in reference to
the metric equivalent. A Megapixel does equate to 1,000,000 pixels, an
internet connection of 56 kbps is 56,000 bits per second. Once again a
confusing point regarding computers. So here is the chart for the prefixes
for digital files:
Prefix 
Power of 2^{x} 
Abbreviation 
Decimal Equivalent 
exa 
2^{60} 
E 
1,152,921,504,606,850,000 
peta 
2^{50} 
P 
1,125,899,906,842,620 
tera 
2^{40} 
T 
1,099,511,627,776 
giga 
2^{30} 
G 
1,073,741,824 
mega 
2^{20} 
M 
1,048,576 
kilo 
2^{10} 
k 
1,024 
