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 |
|
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 |
µ (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) |