The trit, ban, and nat are rarely used to measure storage capacity; but the nat, in particular, is often used in information theory, because natural logarithms are mathematically more convenient than logarithms in other bases.
Several conventional names are used for collections or groups of bits.
Computers usually manipulate bits in groups of a fixed size, conventionally called words. The number of bits in a word is usually defined by the size of the registers in the computer's CPU, or by the number of data bits that are fetched from its main memory in a single operation. In the IA-32 architecture more commonly known as x86-32, a word is 32 bits, but other past and current architectures use words with 4, 8, 9, 12, 13, 16, 18, 20, 21, 22, 24, 25, 29, 30, 31, 32, 33, 35, 36, 38, 39, 40, 42, 44, 48, 50, 52, 54, 56, 60, 64, 72 bits or others.
A unit for a large amount of data can be formed using either a metric or binary prefix with a base unit. For storage, the base unit is typically byte. For communication throughput, a base unit of bit is common. For example, using the metric kilo prefix, a kilobyte is 1000 bytes and a kilobit is 1000 bits.
Use of metric prefixes is common, but often inaccurate since binary storage hardware is organized with capacity that is a power of 2 – not 10 as the metric prefixes are. In the context of computing, the metric prefixes are often intended to mean something other than their normal meaning. For example, 'kilobyte' often refers to 1024 bytes even though the standard meaning of kilo is 1000. Also, 'mega' normally means one million, but in computing is often used to mean 220 = 1048576. The table below illustrates the differences between normal metric sizes and the intended size – the binary size.
Some notable unit names that are today obsolete or only used in limited contexts.
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