Explaining Si Unit For Computer Storage
Most of us who use computers either in our personal or professional lives will be
familiar with the idea of computer storage and some of the units which are used to designate storage capacity at the lower end of the spectrum. The following article provides an overview of all of the units that have, as of present, been classified as SI units (International System of Units) including the familiar kilo-, mega- and gigabytes.
Before looking at its multiples it is worth becoming familiar with the concept of a byte (B) and what it represents. The fundamental unit of computer information storage is actually a bit (short for a binary digit) which is a binary concept in that it exist in one of two states, 1 or 0. A byte in turn is derived from eight bits because that was generally the number needed to form the smallest unit of meaningful data - a single character of text. Therefore, a byte is usually now equivalent to an octet of bits although it can and has varied depending on the hardware in question. The word itself actually originated in 1956 as an intentionally incorrect spelling of the word bite to avoid corruption back to its smaller constituent, the bit.
Bytes can be measured in decimal (multiples of ten) or binary (multiples of two), again depending on the manufacturer of the hardware in question and unofficial convention. The following are decimal multiples as specified by the SI classification but the binary use of the terms is actually far more prevalent in practice. For every 1,000 bytes, the nearest binary equivalent would be 1,024 bytes. As binary systems us the concept of two states (e.g., true/false, off/on, 1/0, positive/negative) to represent information the binary multiples use doubling rather than factors of ten. To achieve the nearest equivalent value to 1,000 therefore the sequence 2, 4, 8, 16, 32, 64, 128, 256, 512, 1,024 is used; 1,024 being two to the power of ten (i.e., 210). At the lower end of the scale, binary and decimal equivalents are fairly close to each other (1,000 vs 1,024 is different by 2.4%), but as the scales grow the difference is magnified to the extent that the nearest equivalent multiples are almost 21% apart when considering 280 and 1024.
To avoid confusion between decimal and binary values, binary specific units have been standardised by the International Electrotechnical Commission (IEC) although the SI terms are still most frequently used to refer to the binary values.
Kilobyte
kB (KB for binary)
Number of bytes:
Decimal - 103
Binary - 210
Difference between decimal and binary figures - 2.40%
IEC equivalent:
Prefix - Kibi-
Symbol - KiB
Example Storage: A text file of approximately 150 words (i.e., approx 1,000 characters)
First Used: kilo- 1940s; kilobyte circa mid 1960s
Megabyte
MB
Number of bytes:
Dec. - 106
Bin. - 220
Diff. - 4.86%
IEC:
Mebi-
MiB
Example Storage:
A text file/book of approximately 500 pages of 2,000 characters per page.
(If 8 bits per pixel, i.e., 256 colour depth) A 1,024x1,024 resolution image
First Used: mega- 1940s
Gigabyte
GB
Number of bytes:
Dec. - 109
Bin. - 230
Diff. - 7.37%
IEC:
Gibi-
GiB
Example Storage: One hour of standard definition video
First Used: giga- defined in 1960
Terabyte
TB
Number of bytes:
Dec. - 1012
Bin. - 240
Diff. - 9.95%
IEC:
Tebi-
TiB
Example Storage: Around 17,000 hours of compressed audio
First Used: terra- defined in 1960
Petabyte
PB
Number of bytes:
Dec. - 1015
Bin. - 250
Diff. - 12.59%
IEC:
Pebi-
PiB
Example Storage: The entire video storage of Netflix
First Used: peta- defined in 1975
Exabyte
EB
Number of bytes:
Dec. - 1018
Bin. - 260
Diff. - 15.29%
IEC:
Exbi-
EiB
Example Storage:
Estimated internet traffic per day in 2010
Estimated
cloud hosting capacity of Amazon
First Used: exa- defined in 1975
Zettabyte
ZB
Number of bytes:
Dec. - 1021
Bin. - 270
Diff. - 18.06%
IEC:
Zebi-
ZiB
Example Storage: All human speech ever spoken could be stored as an estimated 42ZB of compressed audio
First Used: zetta- defined in 1991
Yottabyte
YB
Number of bytes:
Dec. - 1024
Bin. - 280
Diff. - 20.89%
IEC:
Yobi-
YiB
Example Storage:
All human speech in approx. 0.042 YB
By some estimations the entire digital data stored on earth
First Used: yotta- defined in 1991
by: Stuart Mitchell
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