V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

HDM
       Hardware Device Module (I2O)


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

Hierarchical Design Methodology
HDM

    (HDM) A method for specifying software and
   systems using hierarchies of abstract machines, developed by
   Larry Robinson at SRI International circa 1975-1976.  The
   specifications were written in SPECIAL.

   (2012-07-08)