This paper presents a comparative study of the performance of three operating systems that run on the personal computer archi-tecture derived from the IBM-PC, The operating systems, Windows for Workgroups, Windows NT, and NetBSD (a freely available variant of the UNIX operating system), cover a broad range ofs ystem functionalist y and user requirements, from a single address space model to full protection with preemptive multi-tasking. Our measurements were enabled by hardware counters in Intel’s Pentium processor that permit measurement of a broad range of processor events including instruction counts and on-chip cache miss counts. We used both microbenchmarks, which expose specific differences between the systems, and application workloads, which provide an indication of expected end-to-end performance. Our microbenchmark results show that accessing system functionality is often more expensive in Windows for Workgroups than in the other two systems due to frequent changes in machine mode and the use of system call hooks. When running native applications, Windows NT is more efficient than Windows, but it incurs overhead similar to that of a microkemel since its application interface (the Wln32 API) is implemented as a user-level server. Overall, system functionality can be accessed most efficiently in NetBSD; we attribute this to its monolithic structure, and to the absence of the complications created by hardware backwards compatibility requirements in the other systems. Measurements of application performance show that although the impact of these differences is significant in terms of instruction counts and other hardware events (often a factor of 2 to 7 difference between the systems), overall performance is sometimes determined by the functionality provided by specific subsystems, such as the graphics subsystem or the file system buffer cache. 1.

We are currently involved in research to enable PVM to take advantage of shared networks of workstations (NOWs) more effectively. In such a computing environment, it is important to utilize workstations unobtrusively and recover from machine failures. Towards this goal, we have enhanced PVM with transparent task migration, checkpointing, and global scheduling. These enhancements are part of the MIST project which takes an open systems approach in developing a cohesive, distributed parallel computing environment. This open systems approach promotes plug-and-play integration of independently developed modules, such as Condor, DQS, AVS, Prospero, XPVM, PIOUS, Ptools, etc. Transparent task migration, in conjunction with a global scheduler, facilitates the use of shared NOWs by allowing parallel jobs to unobtrusively utilize nodes that are currently unused. PVM tasks can be moved onto nodes that are otherwise idle, and moved off when the node is no longer free. Experiments show that migrati...

Computational grids provide computing power by sharing resources across administrative domains. This sharing, coupled with the need to execute untrusted code from arbitrary users, introduces security hazards. This paper addresses the security implications of making a computing resource available to untrusted applications via computational grids. It highlights the problems and limitations of current grid environments and proposes a technique that employs runtime monitoring and a restricted shell. The technique can be used for setting-up an execution environment that supports the full legitimate use allowed by the security policy of a shared resource. Performance analysis shows up to 2.14 times execution overhead improvement for shellbased applications. The approach proves effective and provides a substrate for hybrid techniques that combine static and dynamic mechanisms to minimize monitoring overheads.

Traditional operating system architectures are not able to cope with the demands of ubiquitous computing. These demands include mobility of code and running applications, precise resource control, robustness, and user-friendly failure handling. Furthermore, traditional operating systems were designed for desktop or server use and contain functionality that is ballast for a ubiquitous system. One example for such ballast is the file system. We describe JX, our own operating system architecture, that has the desired properties, follows a microkernel approach, and structures the operating system as a set of components. 1