From its inception, the WSR-88D Program has recognized the need for system enhancement and growth. Under the NEXRAD Product Improvement (NPI) project, the National Severe Storms Laboratory (NSSL) designed and demonstrated an open-system architecture for the Radar Data Acquisition (RDA) subsystem of the WSR-88D radar. One of the objectives of the first phase of the open RDA (ORDA) project consisted of replacement of the signal processing subsystem (SPS) and the RDA status and control computer (RDASC) with a modern flexible and scalable system. Legacy Hardwired Signal Processor (HSP) and Programmable Signal Processor (PSP) functionalities were successfully migrated to a multiprocessor environment suitable for this type of application. This paper presents general characteristics and functional allocation of the SPS in the new open-systems design.