Abstract: With the functions of data processing and file management,a peripheral subsystem and convenient APL,the DOS system has become a widely applied operating system for PCs and compatible computers.Normally,DOS can not be used with real time,multi-task systems.Using the Terminate and Stay Resident (TSR) technique,a real time,multi-task system for a paper mill was designed for a DOS environment.Through analyzing the DOS kernel,five aspects of real time,multitask problems are solved by means of TSR.