a note on the use of MBps, kiB etc.

Bits and bytes, kilo, mega, and their abbreviations. This page attempts to explain both the correct, and the common usage of these terms. Note that the two are not necessarily the same.

In abbreviations, a capital "B" signifies a Byte (usually an 8-bit word, although according to the IEEE definition, on a 16-bit architecture, a byte may mean a 16-bit word), whereas the lowercase signifies a bit. This is infrequently adhered to, but seems to be the only attempt at standardisation.

The SI prefixes always signify the powers of 10. That is kilo means one thousand, mega means one million, giga means one billion (and note here I mean an SI billion, 10^9, and not an old-english billion, which was a million millions).

However, you should be aware that computer programmers, and memory manufacturers/vendors often use kilo to mean 1024 this is because 1024 = 2^10. Memory is addressed in a binary manner, so it is desirable to organise and access memory in chunks whose length are a power of two.

In December 1998, the IEC made an approval to differentiate between 1024 bytes and 1 kilobyte by the definition of a new term, a kibibyte (kilo-binary byte). See http://physics.nist.gov/cuu/Units/binary.html

Also, 1MiB, a Mebibyte, is 1024 x 1024 bytes, = 1048576 bytes. These unusual prefixes are used in preference to the abuse of SI prefixes by a few people. The majority either follow no standard, or abuse the SI terms. I prefer in my writing to use these terms and prefixes for clarity and accuracy.

Note that:

• A memory chip sold as 1MB is usually actually a 1.048576MB (1MiB) memory.
• A hard drive sold as 20GB is truly 20,000,000,000 Bytes.
• A file size reported by windows as 16kB is actually 16384 Bytes (16kiB)
• A transfer rate of 1Mbps is 10^6 bits per second

Further, under traditional (ab)use of the terms, a wave file reported by windows as 160kB occupies 163.84kB of disk space, but when loaded into memory, occupies only 160kB. Yet when played back at a rate of 10kBps, takes around 16.4 seconds to complete.