Spring 2000 Midterm Solutions

Spring 2000 Midterm Solutions - Spring 2000 Midterm...

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Spring 2000 Midterm Solutions 1. A real-time system is used when there is a rigid time requirement in the operation. For example, for medical equipment, traffic lights, computer systems for cars, etc. There are two types of real-time systems. A hard real-time systems deal with critical tasks that should be completed on time while soft real-time systems deal with critical tasks that get the highest priority until completion. 2. In kernel mode, the system has access to an extended set of instructions, it can modify the interrupt vector, and can modify any section of memory. In user mode, the system has access to only a restricted set of instructions, cannot modify the interrupt vector, and has access to a restricted range of memory. 3. Modern CPU's have kernel and user mode because of reliability and security. Reliability because the user program can crash without crashing other programs. Security because different user processes are kept separate, and resources can be protected by unwanted users. 4. System calls use software interrupts because software interrupts allow switching from user to kernel mode. System calls is the way to access operating system services and need to run in kernel mode. In kernel mode, the system will have access to the interrupt vector and the memory it will need to perform its operations. 5. Steps for servicing an interrupt a. interrupt b. save registers, program counter, return address, etc. c. go to interrupt vector and jump to address corresponding to that
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Spring 2000 Midterm Solutions - Spring 2000 Midterm...

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