Richard 'RMS' Stallman
's answer to the POSIX Central Comittee
's decision to make the POSIX
standard data size unit 512 byte
s (=1 block).
In spite of the decision, RMS declared the standard unit in the GNU system would be 1 kilobyte. Till this day, it is so for the GNU file utils' (du, df...). POSIX compatibility could still be achieved by setting the environment variable POSIX_ME_HARDER.
Later on, POSIX_ME_HARDER was changed to POSIXLY_CORRECT.