Fault tolerant networks of workstations

Networks of workstations make cheap and powerful parallel processors and many systems have been demonstrated using Unix workstations. Personal computers, with their cheap, high performance CPUs, can also be used in a similar way. However, if we are to exploit the multitudes of PCs that sit on desks idle for much of the time, we need robust systems. The uncontrolled environment and physical separation between elements of the parallel system make them prone to a variety of faults that would not normally plague a single processor in a machine room. We describe extensions made to the run-time system for Old MacDonald-a network of PowerPC based Macintoshes-to enable programs written in a functional style using Cilk-a threaded extension of C-to continue in the face of processor and network failures and unpredictable delays likely to be encountered when using widely dispersed machines as components of a parallel system.