The introduction of concurrency into programs has added to the complexity of the software design process. This is most evident in the design of communications protocols where concurrency is inherent to the behavior of the system. The complexity exhibited by such software systems makes more evident the need for computer-aided tools for automatically analyzing behavior.

The use of micro-processors and commercial operating systems in real-time applications demands a good understanding of factors which influence software performance. Advances in micro-processor design (e.g. pipelining) make performance prediction based on instruction cycle counts difficult. In addition, the increasing complexity of operating systems raises doubts about our ability to ensure that their performance will meet system requirements. Performance measurement is more important than ever. This paper describes an ongoing project intended to use performance measurements to characterize the performance of real-time systems software. To date the project has conducted extensive experiments on an in-house operating system running on Intel's 286/10 micro-computer in order to test the feasibility of accurate and repeatable measurement of O/S performance. The measurement approach, which views the software from a resource-consumption standpoint, can be applied to both O/S and application level software. Some of the measurement results are presented here and are used to test the manufacturer's assumptions about the hardware's performance.

An environment to support designers in the modeling, analysis, and simulation of concurrent systems is described. It is shown how a fully nested structure model supports multilevel design and focuses attention on the interfaces between the modules which serve to encapsulate behavior. Using simple examples, it is shown how a formal graph model can be used to model behavior in three domains: control flow, data flow, and interpretation. The effectiveness of the explicit environment model in SARA is discussed and the capability to analyze correctness and evaluate performance of a system model is demonstrated. A description of the integral help designed into SARA shows how the designer can be offered consistent use of any new tool introduced to support the design process.

This paper models the CCITT X.21 interface specification using a graph model and verifies the behavior of the interface using analysis tools accessible through UCLA's SARA (System Architects' Apprentice) design aid system. Behavior of the interface is modeled in three domains: control flow, data flow, and interpretation. Explicit models of assumed behavior for the environment and for the system under study are incorporated in a SARA world view such that systematic analysis and simulation can be applied.