The implementation of data modems by means by commercially available general-purpose microprocessors is discussed. A number of signal-processing methods are given which reduce and simplify the arithmetical operations in both the transmitter and receiver. It is shown that with these methods sufficient computation time can be gained to enable the use of gneeral-purpose microprocessors for the design of versatile data modems for bitspeeds up to 9600 bits/s and even higher.