Questions and Answers of Computer Engineering

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What are the three main purposes of an operating system?

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List the four steps that are necessary to run a program on a completely dedicated machine.

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What is the main advantage of multiprogramming?

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What are the main differences between operating systems for mainframe computers and personal computers?

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In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security

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Define the essential properties of the following types of operating systems: a. Batch b. Interactive c. Time sharing d. Real time e. Network f.

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We have stressed the need for an operating system to make efficient use of the computing hardware. When is it appropriate for the operating system to

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Under what circumstances would a user be better off using a time-sharing system, rather than a personal computer or single-user workstation?

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Describe the differences between symmetric and asymmetric multiprocessing. What are three advantages and one disadvantage of multiprocessor systems?

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What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment?

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Prefetching is a method of overlapping the I/O of a job with that job’s own computation. The idea is simple. After a read operation completes and

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How does the distinction between monitor mode and user mode function as a rudimentary form of protection (security) system?

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What are the differences between a trap and an interrupt? What is the use of each function?

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For what types of operations is DMA useful? Explain your answer.

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Which of the following instructions should be privileged? a. Set value of timer. b. Read the clock. c. Clear memory. d. Turn off interrupts. e.

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Some computer systems do not provide a privileged mode of operation in hardware. Consider whether it is possible to construct a secure operating

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Some early computers protected the operating system by placing it in a memory partition that could not be modified by either the user job or the

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Protecting the operating system is crucial to ensuring that the computer system operates correctly. Provision of this protection is the reason behind

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Give two reasons why caches are useful. What problems do they solve? What problems do they cause? If a cache can be made as large as the device for

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Writing an operating system that can operate without interference from malicious or undebugged user programs requires some hardware assistance. Name

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What are the five major activities of an operating system in regard to process management?

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What are the three major activities of an operating system in regard to memory management?

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What are the three major activities of an operating system in regard to secondary-storage management?

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What are the five major activities of an operating system in regard to file management?

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What is the purpose of the command interpreter? Why is it usually separate from the kernel?

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List five services provided by an operating system. Explain how each provides convenience to the users. Explain also in which cases it would be

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What is the purpose of system calls?

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Using system calls, write a program in either C or C++ that reads data from one file and copies it to another file. Such a program was described in

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Why does Java provide the ability to call from a Java program native methods that are written in, say, C or C++? Provide an example where a native

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What is the purpose of system programs?

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What is the main advantage of the layered approach to system design?

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What are the main advantages of the microkernel approach to system design?

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What is the main advantage for an operating-system designer of using a virtual-machine architecture? What is the main advantage for a user?

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Why is a just-in-time compiler useful for executing Java programs?

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Why is the separation of mechanism and policy a desirable property?

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The experimental Synthesis operating system has an assembler incorporated within the kernel. To optimize system-call performance, the kernel

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MS-DOS provided no means of concurrent processing. Discuss three major complications that concurrent processing adds to an operating system.

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Describe the differences among short-term, medium-term, and long-term scheduling.

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A DECSYSTEM-20 computer has multiple register sets. Describe the actions of a context switch if the new context is already loaded into one of the

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Describe the actions a kernel takes to context switch between processes.

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Provide two programming examples of multithreading giving improved performance over a single-threaded solution.

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Provide two programming examples of multithreading that would not improve performance over a single-threaded solution.

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What are two differences between user-level threads and kernel-level threads? Under what circumstances is one type better than the other?

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Describe the actions taken by a kernel to context switch between kernel-level threads.

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Describe the actions taken by a thread library to context switch between user-level threads.

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What resources are used when a thread is created? How do they differ from those used when a process is created?

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A CPU scheduling algorithm determines an order for the execution of its scheduled processes. Given n processes to be scheduled on one processor, how

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Define the difference between preemptive and nonpreemptive scheduling. State why strict nonpreemptive scheduling is unlikely to be used in a computer

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Consider the following set of processes, with the length of the CPU-burst time given in milliseconds:

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Suppose that the following processes arrive for execution at the times indicated. Each process will run the listed amount of time. In answering the

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Consider a variant of the RR scheduling algorithm where the entries in the ready queue are pointers to the PCBs. a. What would be the effect of

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What advantage is there in having different time-quantum sizes on different levels of a multilevel queuing system?

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Consider the following preemptive priority-scheduling algorithm based on dynamically changing priorities. Larger priority numbers imply higher

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Many CPU scheduling algorithms are parameterized. For example, the RR algorithm requires a parameter to indicate the time slice. Multilevel feedback

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Suppose that a scheduling algorithm (at the level of short-term CPU scheduling) favors those processes that have used the least processor time in the

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Why does Solaris 2 implement multiple locking mechanisms? Under what circumstances does it use spin locks, semaphores, adaptive mutexes, conditional

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Explain the differences in the degree to which the following scheduling algorithms discriminate in favor of short processes: a. FCFS b. RR c.

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List three examples of deadlocks that are not related to a computer-system environment

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Is it possible to have a deadlock involving only one single process? Explain your answer.

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Consider a system consisting of four resources of the same type that are shared by three processes, each of which needs at most two resources. Show

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Consider a system consisting of m resources of the same type, being shared by n processes. Resources can be requested and released by processes only

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Consider the following resource-allocation policy. Requests and releases for resources are allowed at any time. If a request for resources cannot be

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Explain the difference between internal and external fragmentation.

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Describe the following allocation algorithms: a. First fit b. Best fit c. Worst fit

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When a process is rolled out of memory, it loses its ability to use the CPU (at least for a while). Describe another situation where a process loses

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Given memory partitions of 100K, 500K, 200K, 300K, and 600K (in order), how would each of the First-fit, Best-fit, and Worst-fit algorithms place

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Why are page sizes always powers of 2?

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Consider a logical address space of eight pages of 1024 words each, mapped onto a physical memory of 32 frames. a. How many bits are there in the

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On a system with paging, a process cannot access memory that it does not own; why? How could the operating system allow access to other memory? Why

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Consider a paging system with the page table stored in memory. a. If a memory reference takes 200 nanoseconds, how long does a paged memory

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What is the effect of allowing two entries in a page table to point to the same page frame in memory? Explain how this effect could be used to

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Why are segmentation and paging sometimes combined into one scheme?

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Describe a mechanism by which one segment could belong to the address space of two different processes.

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Explain why it is easier to share a reentrant module using segmentation than it is to do so when pure paging is used.

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Consider the following segment table:

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Consider the Intel address translation scheme shown in Figure 9.20. a. Describe all the steps that the Intel 80386 takes in translating a logical

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Under what circumstances do page faults occur? Describe the actions taken by the operating system when a page fault occurs.

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Assume a page reference string for a process with m frames (initially all empty). The page reference string has length p with n distinct page numbers

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A certain computer provides its users with a virtual-memory space of 232 bytes. The computer has 218 bytes of physical memory. The virtual memory is

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Which of the following programming techniques and structures are “good” for a demand paged environment? Which are “not good”? Explain your

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Assume we have a demand-paged memory. The page table is held in registers. It takes 8 milliseconds to service a page fault if an empty page is

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Consider the following page-replacement algorithms. Rank these algorithms on a five point scale from “bad” to “perfect” according to their

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When virtual memory is implemented in a computing system, there are certain costs associated with the technique and certain benefits. List the costs

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An operating system supports a paged virtual memory, using a central processor with a cycle time of 1 microsecond. It costs an additional 1

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Consider a demand-paging system with the following time-measured utilizations: CPU utilization 20% Paging disk 97.7% Other I/O devices

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Consider the following page reference string: 1, 2, 3, 4, 2, 1, 5, 6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3, 6 How many page faults would occur for the

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Suppose that you want to use a paging algorithm that requires a reference bit (such as second-chance replacement or working-set model), but the

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Segmentation is similar to paging but uses variable-sized “pages.” Define two segment replacement algorithms based on FIFO and LRU

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A page-replacement algorithm should minimize the number of page faults. We can do this minimization by distributing heavily used pages evenly over

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Consider a demand-paging system with a paging disk that has an average access and transfer time of 20 milliseconds. Addresses are translated through

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Consider a demand-paged computer system where the degree of multiprogramming is currently fixed at four. The system was recently measured to

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We have an operating system for a machine that uses base and limit registers, but we have modified the machine to provide a page table. Can the page

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What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

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What problems arise if the directory structure is a general graph?

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What is garbage collection?

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How can we protect files on a single-user system?

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What might damage files?

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List kinds of access we might want to limit on a multi user system.

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List four ways systems might provide for users to protect their files against other users.

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In the IBM/370, memory protection is provided through the use of keys. A key is a 4-bit quantity. Each 2K block of memory has a key (the storage key)

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