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

SoftModem

   The integration of modem controller and data pump
   algorithms into a single RAM-based DSP hardware
   architecture.  These integrated algorithms are stored on the
   computer's hard disk, from which they are downloaded into the
   DSP board's random-access memory (RAM).  This downloading, or
   "booting" process of the PC-installed software algorithms
   occurs as part of the computer's power-up initialisation
   process in less than 100 milliseconds, making it transparent
   to the user.

   [Digicom Modem FAQ version 2.03].