The kilobyte, unit of digital data

The kilobyte is 1000 bytes, written kB with a lowercase k and a capital B. A page of plain text is a few kilobytes, and a text message carries 140 bytes, so a single kilobyte holds seven of them.

The letter that matters is the second one. kB with a capital B is the kilobyte, kb with a lowercase b is the kilobit, and a byte is eight bits: the two differ by a factor of eight, which is why a line sold at 100 Mb/s downloads at 12.5 MB/s at best. The capital K, seen everywhere as KB, is a third habit: the international system writes kilo with a lowercase k, and the capital was borrowed from the 1024 counting that the IEC renamed kibibyte in 1998. The 1.44 MB floppy disk shows the confusion at its worst, since it held 1440 blocks of 1024 bytes, which is neither 1.44 million bytes nor 1.44 mebibytes.

The kilobyte in other units

Digital storage