International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / NASA's ground telemetry data systems developed by the Microelectronics Systems Branch at the Goddard Space Flight Center, use a generic but expandable architecture known as the "Functional Components Approach." This approach is based on the industry standard VMEbus and makes use of multiple commercial and custom VLSI hardware based cards to provide standard off-the-shelf telemetry processing functions (e.g., frame synchronization, packet processing, etc.) for many telemetry data handling applications. To maintain maximum flexibility and performance of these systems, a special real-time system environment has been developed, the Modular Environment for Data Systems (MEDS). Currently, MEDS comprises over 300,000 lines of tested and operational code based on a non-UNIX real-time commercial operating system. To provide for increased functionality and adherence to industry standards, this software is being transformed to run under a UNIX-compatible real-time environment. This effort must allow for existing systems and interfaces and provide exact duplicates of the system functions now used in the current real-time environment. Various techniques will be used to provide a relatively quick transition to this new real-time operating system environment. Additionally, all standard MEDS card to card and system to system interfaces will be preserved, providing for a smooth transition and allowing for telemetry processing cards that have not yet been converted to reside side-by-side with cards that have been converted. This paper describes this conversion effort.