Most MIMD multiprocessors today are configured with two distinct types of processor nodes: those that have disks attached, which are dedicated to file I/O, and those that do not have disks attached, which are used for running applications. Several architectural trends have led some to propose configuring systems so that all processors are used for application processing, even those with disks attached. We examine this idea experimentally, focusing on the impact of remote I/O requests on local computational processes. We found that in an efficient file system the I/O processors can transfer data at near peak speeds with little CPU overhead, leaving substantial CPU power for running applications. On the other hand, we found that some complex file-system features could require substantial CPU overhead. Thus, for a multiprocessor system to obtain good I/O and computational performance on a mix of applications, the file system (both operating system and libraries) must be prepared to adapt their policies to changing conditions.