ZEN is a CORBA ORB designed to support distributed, real-time, and embedded (DRE) applications that have stringent memory constraints. This paper discusses the design and performance of ZENs portable object adapter (POA) which is an important component in a CORBA object request broker (ORB). This paper makes the following three contributions to the study of middleware for memory-constrained DRE applications. First, it presents three alternative designs of the CORBA POA. Second, it explains how design patterns can be applied to improve the quality and performance of POA implementations. Finally, it presents empirical measurements based on the ZEN ORB showing how memory footprint can be reduced significantly while throughput is comparable to a conventional ORB implementation.