Make your own free website on Tripod.com

Binary Data Storage Terms

There are various names used to refer to various groupings of bits of data. Most people know that 8 bits is a byte, but there are many other terms in universal use. These are not always totally universal, but they are the most common definitions to my knowledge:

Term

Number of Bits

bit / digit / flag

1

nibble / nybble

4

byte / character

8

word

16

double word / long word

32

very long word

64

  

Powers of Two With Common Designations

The chart below shows the powers of two from 0 to 40. PC numbers tend to be based on powers of 2 because of the way computers use the binary number system to encode information. I have also shown the most common designation used to match to each number, which you can use as a cross-reference if you ever need to know exactly how many bytes 16 MB is, for example. For an explanation of the storage abbreviations, see here.

n

2^n

Common Storage
Designation (Bytes)

0

1

1 byte

1

2

2 bytes

2

4

4 bytes

3

8

8 bytes

4

16

16 bytes

5

32

32 bytes

6

64

64 bytes

7

128

128 bytes

8

256

256 bytes or 0.25 KB

9

512

512 bytes or 0.5 KB

10

1,024

1 KB

11

2,048

2 KB

12

4,096

4 KB

13

8,192

8 KB

14

16,384

16 KB

15

32,768

32 KB

16

65,536

64 KB

17

131,072

128 KB

18

262,144

256 KB or 0.25 MB

19

524,288

512 KB or 0.5 MB

20

1,048,576

1 MB

21

2,097,152

2 MB

22

4,194,304

4 MB

23

8,388,608

8 MB

24

16,777,216

16 MB

25

33,554,432

32 MB

26

67,108,864

64 MB

27

134,217,728

128 MB

28

268,435,456

256 MB or 0.25 GB

29

536,870,912

512 MB or 0.5 GB

30

1,073,741,824

1 GB

31

2,147,483,648

2 GB

32

4,294,967,296

4 GB

33

8,589,934,592

8 GB

34

17,179,869,184

16 GB

35

34,359,738,368

32 GB

36

68,719,476,736

64 GB

37

137,438,953,472

128 GB

38

274,877,906,944

256 GB or 0.25 TB

39

549,755,813,888

512 GB or 0.5 TB

40

1,099,511,627,776

1 TB

 

Binary and Decimal Byte "Equivalents"

One of the strange coincidences in the computer world is that every tenth power of two is approximately equal to every third power of ten. This has resulted in two different definitions of various size prefixes: "kilobyte" and "megabyte", etc. can mean one of two different things depending on context. This situation can cause confusion, especially in respect to hard disk size measurements, where often, both measurements are used; see here for more details.

The IEEE has proposed a new naming convention for the binary numbers, to eliminate the confusion inherent in having the different binary and decimal numbers use the same names. You can read more about this proposal in detail here. The proposed new naming convention is listed below under the columns "Binary Name" and "Binary Abbr." Of course, right now most people use the decimal names and abbreviations for both the decimal and binary numbers.

Decimal Name

Decimal Abbr.

Decimal Power

Decimal Value

Binary Name

Binary Abbr.

Binary Power

Binary Value

Kilobyte

kB

10^3

1,000

Kibibyte

kiB

2^10

1,024

Megabyte

MB

10^6

1,000,000

Mebibyte

MiB

2^20

1,048,576

Gigabyte

GB

10^9

1,000,000,000

Gibibyte

GiB

2^30

1,073,741,824

Terabyte

TB

10^12

1,000,000,000,000

Tebibyte

TiB

2^40

1,099,511,627,776

 

Standard Metric (SI) Prefixes, Values and Common Usage

There are many different size prefixes that are used to denote large and small numbers. The standard prefixes, from one trillion to one trillionth, are denoted below, along with some of the common places in the computer world where you will see them used:

Name

Abbr.

Decimal Power

Factor

Common Usage

tera

T

10^12

1,000,000,000,000

large data warehouses (TB)

giga

G

10^9

1,000,000,000

mass storage (GB), CPU speed (GHz)

mega

M

10^6

1,000,000

storage (MB), memory (MB), CPU speed (MHz), others

kilo

K

10^3

1,000

memory (KB), communication speed (KB/sec), others

milli

m

10^-3

0.001

drive access speed (ms)

micro

(Greek "mu")

10^-6

0.000001

various circuit speeds (us)

nano

n

10^-9

0.000000001

memory speed (ns), CPU cycle length (ns), capacitors (nF)

pico

p

10^-12

0.000000000001

capacitors (pF)