Some shells also exclusively read/write to the history file, and not keep it in memory. that really makes things entertaining, because when running two shells running as the same user, "!!" is not always what you think it's going to be! for example: shell 1: ls /dev shell 2: ls /tmp shell 1: !! == ls /tmp Oops! but it can be a good thing sometimes. it grows on you after awhile.
