Control systems based on embedded DSP boards often require specialized programming and development tools, lack interoperability with standardized architectures and tools, lack flexibility when computational requirements change, and are often relatively expensive. A potentially attractive alternative is to implement the control system using RT-Linux, a free modification to Linux intended to support hard real-time computation. The combination of RT-Linux and commodity PCs offer low-cost development that results in flexible and reusable code that satisfies performance requirements. This paper describes a case study in the use of RT-Linux for implementing a control system for a high speed magnetic bearing system. Experiences designing the software architecture, defining the timing requirements of the control tasks, implementing the control tasks in RT-Linux, and measuring the predictability of RT-Linux for this application are discussed. Insights provided by the paper can be used as guidelines for other hard real-time system developers considering using RT-Linux.