Operating System Support for Multi-User, Remote, Graphical Interaction

The emergence of thin client computing and multi-user, remote, graphical interaction revives a range of operating system research issues long dormant, and introduces new directions as well. This paper investigates the effect of operating system design and implementation on the performance of thin client service and interactive applications. We contend that the key performance metric for this type of system and its applications is user-perceived latency and we give a structured approach for investigating operating system design with this criterion in mind. In particular, we apply our approach to a quantitative comparison and analysis of Windows NT, Terminal Server Edition (TSE), and Linux with the X Windows System, two popular implementations of thin client service. We find that the processor and memory scheduling algorithms in both operating systems are not tuned for thin client service. Under heavy CPU and memory load, we observed user-perceived latencies up to 100 times beyond the threshold of human perception. Even in the idle state, these systems induce unnecessary latency. TSE performs particularly poorly despite scheduler modifications to improve interactive responsiveness. We also show that TSE's network protocol outperforms X by up to six times, and also makes use of a bitmap cache which is essential for handling dynamic elements of modern user interfaces and can reduce network load in these cases by up to 2000%.