Partitioning of function in a distributed graphics system (computer networks, operating, window)
William I. Nowicki · 1985
Although recent advances in graphics workstations promise much computing power for the future needs of researchers, traditional approaches to software organization waste much of this power. Most systems treat the workstation as either a fixed-function terminal or a self-contained personal computer; these roles have limitations that can be overcome by considering the workstation a multi-function component of a distributed system. Traditional standard graphics packages and object-oriented window systems offer important functionality, but a third approach, virtual terminal management systems, is more appropriate for a distributed operating system. The Stanford Distributed Systems Group has implemented such a distributed system for graphics workstations, organized as a collection of servers providing services to clients. Major issues are how to partition functions between the server and its clients, and physically partition the server. In particular, the service that displays graphical objects is called the Virtual Graphics Terminal Service (VGTS). The VGTS architecture is described, as well as a prototype implementation. This thesis discusses the trade-offs involved in partitioning of function in a distributed graphics system. Performance is one important property traded for advanced functionality or decreased cost. To provide adequate performance in a distributed system, communication costs should be kept low, as well as the frequency of the communication. By providing modeling as well as viewing facilities, the VGTS reduces the communication required between applications and the service. Measurements verify that performance is insensitive to network bandwidth, but depends heavily on CPU speed and protocol characteristics. Using structure provides important speed improvements in some cases, but other basic factors such as inner loop optimization and proper batching of requests make even larger differences. Finally, conclusions are drawn regarding the partitioning approaches taken in the VGTS. The VGTS is suitable for a large class of applications that perform graphics as an aid to user interface, and is portable to a wide range of powerful workstations. Moreover, the VGTS can be used as a basis for further research on many open questions in distributed systems.