It definitely does write all of the directory area
(boot record,
FAT(s), DIR).
If the /Q option is active (now default?) then that is ALL that it does.
Later versions of DOS also do one additional interesting thing... they copy
the reserved sectors out to the end of the media (or partition for HDs),
where they can used by the UNFORMAT command to magically resuscitate an
accidentally formatted volume. I forget when that started...
Patrick