In 1989 SGS-Thomson and University of Bristol developed a combined GPS/INMARSAT-C terminal, under contract to INMARSAT, who wished to demonstrate the feasibility for the then imminent GMDSS and for fleet-control purposes for trucks. The work was an extension of a fully software GPS receiver design. Moving all the spread-spectrum processing and demodulation into software saved complex hardware, and led to flexibility, both in specification and in the use of the processor. The features of the processor that permitted this flexible use were high speed and high I/O bandwidth. The author discusses the use of this software modulation technique in the GPS, a GSM telephone system, and a generic radio receiver. (5 pages)