The Jargon File (version 4.4.7, 29 Dec 2003):

hard boot
 n.

    See boot.


The Free On-line Dictionary of Computing (30 December 2018):

hard boot

    A boot which resets the entire system.

   The phrase has connations of hostility toward, or frustration
   with, the computer being booted.  For example, "I'll have to
   hard boot this losing Sun", or "I recommend booting it
   hard".

   Hard boots are often performed with a power cycle.

   Contrast soft boot.  See also cold boot and reboot

   [Jargon File]

   (1995-11-27)