Definition: soft modem
Software that performs modem functions using the computer's main CPU rather than in modem hardware. Instead of using a dedicated data pump, programmable DSP chips are used. For example, the PowerPC and Intel's MMX Pentiums have instructions that allow it to perform modem functions.
Many modems themselves are already built as soft modems rather than using chips hardwired to a particular modulation technique. Such modems may be upgradable to new modulation methods with new software that can be downloaded or purchased from the vendor.