A bit is the most commonly unit of data. It represents one of two states - 0 or 1, on or off, yes or no, etc. Commonly used multiples of bits are formed by using SI prefixes, and include:

• 1 nibble = 4 bits
• 1 byte = 8 bits
• 1 KiB (also KB) [kibibyte] = 2¹⁰ bytes = 1024 bytes
• 1 MiB [mibibyte] = 2¹⁰ KiB
• 1 GiB [gibibyte] = 2¹⁰ MiB
• 1 TiB [tibibyte] = 2¹⁰ GiB
• 1 kB [kilobyte] = 1000 bytes
• 1 MB [megabyte] = 1000 KB
• 1 GB [gigabyte] = 1000 MB
• 1 TB [terabyte] = 1000 GB

The International Electrotechnical Commission had issued a standard to distinguish prefixes denoting powers of 10 from those of 2. These units may be used interchangeably at some places (KB in place of kB/KiB, etc); be aware of it.

- extracted from Units of information, Wikipedia as on 1st March 2017