This article presents a comparative study of the performance of three operating systems that run on the personal computer architecture 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 of system functionality and user requirements, from a single-address-space model to full protection with preemptive multitasking. Our measurements are 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 use 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 microkernel, since its application interface (the Win32 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 backward-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.
