CPE 315
Reasons for Multiprocessors
Professor Stearns

• To increase throughput

  Multiple CPUs can run multiple programs faster in a CPU bound environment. An operating system that supports this feature is called a multiprocessing operating system.

• To decrease execution time for a program

  You must write programs as multiple threads using parallel programming algorithms.

• To write programs where the domain is inherently parallel (e.g. a jukebox is inherently 2 threads)
  

  Such programs are known as parallel programs, concurrent programs or multi-threaded programs.
  You can write such programs on a single-cpu machine
      if the language supports multiple threads
      OR the operating system provides a library that supports multiple threads.
  Some languages that support parallel programming: Ada, Java
  Some languages that do not support parallel programming: C, C++, Cobol, Fortran, Pascal, Perl, VB
  

• To provide scalability for the customer

  Most institutions in the U.S operate on one year capital budgets.

• To provide fault tolerence

  e.g. The Space Shuttle software runs on 4 CPUs.