Generic architectures for specific domains can provide significant gains in productivity and quality for real-time systems development. In order to choose among different architectural features, a variety of qualitative criteria have been proposed in the literature. However, real-time systems require a more exact characterization based on quantitative evaluation of some architectural features related to timing properties, such as scalability. In this paper we explore a possible way of using Rate Monotonic Analysis to get a measure of scalability between alternative architectures. The technique is illustrated with a case study in a well-known real-time domain, data acquisition systems. The results show clear differences in scalability for different architectures, giving a clear indication of which one is better from this point of view. We believe that the approach can be used on other properties and domain architectures, thus opening new possibilities for quantitative evaluation of software architectures.