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A bit is a binary digit, written as 0 or 1. A byte is a sequence of eight bits, so 1 B = 8 bit. The letter case matters: lowercase b means bits, while uppercase B means bytes. Prefixes matter too: decimal kB and MB use powers of ten; binary KiB and MiB use powers of two.
What is a bit?
A bit—short for binary digit—is the basic unit in this distinction. It represents one of two possible digit values: 0 or 1. NIST’s binary-prefix reference uses the symbol bit for this unit.
What is a byte?
A byte is a sequence of eight bits, according to the NIST CSRC Glossary. NIST’s binary-prefix reference expresses the relationship as 1 B = 8 bit. A byte is therefore eight times the size of a bit when both are used as units of information.
Why do b and B matter?
The symbol’s capitalization distinguishes the units: b means bit and B means byte. This distinction is useful when reading storage capacities and data rates. For example, a figure written in MB is in megabytes; one written in Mb is in megabits. Convert between them only after identifying the prefix and unit: divide a bit count by eight to get bytes, or multiply a byte count by eight to get bits.
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Are kilobytes 1,000 or 1,024 bytes?
Both figures occur, but they refer to different prefixes. SI prefixes are decimal: kilo means 103, or 1,000. IEC binary prefixes are powers of two: kibi means 210, or 1,024. NIST’s SI prefix guidance says SI prefixes should not be used to indicate powers of two.
| Label | Meaning | Equivalent |
|---|---|---|
| kbit | 1,000 bits | 103 bits |
| Kibit | 1,024 bits | 210 bits |
| kB | 1,000 bytes | 103 bytes |
| KiB | 1,024 bytes | 210 bytes |
| MB | 1,000,000 bytes | 106 bytes |
| MiB | 1,048,576 bytes | 220 bytes |
The binary-prefix reference gives the corresponding larger powers: mega is 106 and mebi is 220; giga is 109 and gibi is 230. Thus, 1 GiB is 230 bytes. The symbols beginning with Ki, Mi, and Gi identify binary prefixes; k, M, and G identify decimal SI prefixes.
Why can a storage capacity look different from a memory figure?
The same informal label has historically been used with different conventions. NIST’s binary-prefix reference describes computing contexts in which “megabyte” could mean 220 bytes, while storage-device manufacturers usually used 1,000,000 bytes. The unambiguous forms are MB for 1,000,000 bytes and MiB for 1,048,576 bytes. Check which convention a quoted capacity uses rather than assuming that every system or device displays it the same way.
How to convert bits and bytes
- Identify the unit. Check whether the value uses bits (b) or bytes (B).
- Identify the prefix. A decimal prefix such as k or M means a power of ten; a binary prefix such as Ki or Mi means a power of two.
- Convert the prefix to the underlying count. For example, 1 MB is 1,000,000 bytes, while 1 MiB is 1,048,576 bytes.
- Convert bits and bytes if needed. Divide bits by eight to obtain bytes; multiply bytes by eight to obtain bits.
For instance, 8,000 bits equal 1,000 bytes, or 1 kB. By contrast, 1 Kibit equals 1,024 bits; dividing by eight gives 128 bytes. Keeping the prefix conversion separate from the bit-to-byte conversion prevents mixing up two different sources of numerical difference.
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What is established about the binary prefixes?
NIST’s binary-prefix reference says the prefixes were first adopted by the International Electrotechnical Commission as Amendment 2 to IEC 60027-2, published in January 1999, and were later incorporated into the second edition of IEC 60027-2, published in November 2000. The NIST web reference does not state its own publication year. NIST’s SI guidance also directs readers to distinguish SI powers of ten from binary prefixes.
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