horizontal encoding

horizontal encoding

   <processor> An {instruction set} where each field (a bit or
   group of bits) in an instruction word controls some
   {functional unit} or {gate} directly, as opposed to {vertical
   encoding} where instruction fields are decoded (by
   {hard-wired} {logic} or {microcode}) to produce the control
   signals.  Horizontal encoding allows all possible combinations
   of control signals (and therefore operations) to be expressed
   as instructions whereas vertical encoding uses a shorter
   instruction word but can only encode those combinations of
   operations built into the decoding logic.

   An {instruction set} may use a mixture of horizontal and
   vertical encoding within each instruction.  Because an
   architecture using horizontal encoding typically requires more
   instruction word bits it is sometimes known as a {very long
   instruction word} (VLIW) architecture.

   (1995-04-23)