8.5 Closing notes

As they drop in price, multiprocessor systems are becoming far more common. These systems have many attractive features, including good price/performance, compatibility with workstations, large memories, high throughput, large shared memories, fast I/O, and many others. While these systems are strong in multiprogrammed server roles, they are also an affordable high performance computing resource for many organizations. Their cache-coherent shared-memory model allows multithreaded applications to be easily developed.

We have also examined some of the software paradigms that must be used to develop multithreaded applications. While you hopefully will never have to write C code with explicit threads like the examples in this chapter, it is nice to understand the fundamental operations at work on these multiprocessor systems. Using the FORTRAN language with an automatic parallelizing compiler, we have the advantage that these and many more details are left to the FORTRAN compiler and runtime library. At some point, especially on the most advanced architectures, you may have to explicitly program a multithreaded program using the types of techniques shown in this chapter.

One trend that has been predicted for some time is that we will begin to see multiple cache-coherent CPUs on a single chip once the ability to increase the clock rate on a single chip slows down. Imagine that your new $2000 workstation has four 1-GHz processors on a single chip. Sounds like a good time to learn how to write multithreaded programs!