The Real-Time Linux operating system was evaluated for implementing real-time digital controllers. Real-Time Linux is flexible and easy to program compared to ordinary digital controllers such as Digital Signal Processor (DSP) and micro-controller. Real-Time Linux was successfully used to control a single-axis hydraulic test rig and a Unimate 2000B six-axis hydraulic robot. Real-Time Linux proved capable of running a six-axis digital controller using floating-point calculations. On a 486-66 MHz Personal Computer (PC), a controller sampling time of 1 ms required less than half the available computation time. The direct and inverse robot kinematics was based on the Denavit-Hartenberg parameters and a straightforward PID six-axis controller proved capable of basic path control. While more sophisticated robot controllers and dynamic compensation would require additional computation power, experiments have shown that they can still be run on the Real-Time Linux system.