1. What is the difference between a process and a thread?

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   A thread contains much less state than does a process, which makes threads cheaper and easier to manipulate than processes. Threads execute within a process, using the process state - such as open files and the address space - to suppliment their own state. Because all threads within a process share the process state, they may use the shared state to communicate among themselves.

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2. What is mutual exclusion? What is a critical region?

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   Mutual exclusion is a form of resource access that ensures that a resource shared among several executing entities (processes or threads) is accessed by only one entity at a time. A critical region is a finite section of an entity's code within which the entity is guaranteed to have mutually exclusive access to a shared resource.

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3. Construct a critical region using semaphores. Don't forget to show the semaphore's initial value.

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   global semaphore mutex = 1
   
   /* other code */
   
   down(mutex) /* enter critical region */
   
   /* access shared resource */
   
   up(mutex) /* leave critical region */
   
   

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4. You are designing an operating system that runs processes without preemption. Do you need to include a scheduler in your system? Explain.

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   Yes you do. Even if a process only releases the CPU when it terminates, the operating system still needs to figure out which process gets the CPU next, and that is what a scheduler does.

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This page last modified on 6 March 2000.