SI Unit Prefix

Prefix

Factor by which the root unit is Multiplied

Letter Symbol

Decimal System

Binary System

Yotta

1 000 000 000 000 000 000 000 000 = 1024

280

Y

Zetta

1 000 000 000 000 000 000 000 = 1021

270

Z

Exa

1 000 000 000 000 000 000 = 1018

260

E

Peta

1 000 000 000 000 000 = 1015

250

P

Tera

1 000 000 000 000 = 1012

240  = 1,099,511,627,776 

T

Giga

1 000 000 000 = 109

230  = 1,073,741,824 

G

Mega

1 000 000 = 106

220  = 1,048,576

M

Kilo

1000 = 103

210  = 1024

K

Hecto

100 = 102

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H

Deka

10 = 101

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DA

Base Unit

1=10 0

2 = 1

 

deci

0.1 = 10-1

 

d

centi

0.01 = 10-2

 

c

milli

0.001 = 10-3

2-10 =1 / 1024

m

micro

0.000 001 = 10-6

2-20 =1 / 1,048,576

µ

nano

0.000 000 001 = 10-9

2-30 =1 / 1,073,741,824 

n

pico

0.000 000 000 001 = 10-12

2-40 =1 / 1,099,511,627,776

p

femto

0.000 000 000 000 001 =10-15

2-50

f

atto

0.000 000 000 000 000 001 = 10-18

2-60

a

zepto

0.000 000 000 000 000 000 001 = 10-21

2-70

z

yocto

0.000 000 000 000 000 000 000 001 = 10-24

2-80

y

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SI Unit

IEEE adopted the International System of Units in 1965 proposed in France 1960 (Systeme International d¡¯Unites)

Quantity                       SI Base Unit                Unit Symbol

length/distance               meter                            m

mass                             kilogram                       kg

time                              second                         sec

electric current              ampere                         A 


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bit -     short for binary digit. In binary system a bit can be either 0 or 1.

Byte - In order to represent  numbers, letters, and special characters, bits are combined into groups of eight bits called bytes. Each byte typically represents one character - in many computers, one addressable storage location. The capacity of main memory is expressed in numbers of bytes.

There are four commonly used units of measurement to describe memory capacity:

One Kilobyte -  abbreviated k, KB, or k-byte - is equivalent to approximately 1000 bytes.

                              (More precisely, 1KB = 1024 bytes = 210 bytes. The older IBM PCs had a top capacity of 640KB, or about 640,000 characters of data.

One Megabyte -  MB or M-byte - represents about 1 million (106) bytes. Precisely 1 KB x 1 KB = 1024 x 1024 =  210 x 210   = 220 =  1048576 bytes.

One Gigabyte -    GB or G-byte - represents about 1 billion (109) bytes. Precisely 1 KB x 1 KB x 1 KB = 1024 x 1024 x 1024 =  210 x 210 x 210   = 230 = 1073741824 bytes.

One Terabyte -    TB or T-byte - represents 1 about trillion (1012) bytes. Precisely 1 KB x 1 KB x 1 KB x 1 KB = 1024 x 1024 x 1024 x 1024 =  210 x 210 x 210 x 210 = 240 = 1099511627776 bytes.