locked and loaded

from Jargon File (4.4.4, 14 Aug 2003)

locked and loaded
 adj.,obs.

   [from military slang for an M-16 rifle with magazine inserted and
   prepared for firing] Said of a removable disk volume properly prepared
   for use -- that is, locked into the drive and with the heads loaded.
   Ironically, because their heads are `loaded' whenever the power is up,
   this description is never used of {Winchester} drives (which are named
   after a rifle).

from The Free On-line Dictionary of Computing (8 July 2008)

locked and loaded

   [Military slang for an M-16 rifle with magazine inserted and
   prepared for firing] Said of a removable disk volume properly
   prepared for use - that is, locked into the drive and with
   the heads loaded.  Ironically, because their heads are
   "loaded" whenever the power is up, this description is never
   used of {Winchester} drives (which are named after a rifle).

   [{Jargon File}]

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