I thought it was "the first PC" however that seems to be wrong
http://www.blinkenlights.com/pc.shtml
http://www.blinkenlights.com/classiccmp/imlac/
and for those interested
http://www.zakon.org/robert/internet/timeline/

it seems to be an arbitrary date used as a convention in programing

on this page it lists that date as the birthday of UNIX
http://www.iee.org/Policy/Areas/SCS/problemdates.cfm
and
http://www.electromagnetic.net/press-releases/unixonegig.php