Questions and Answers of Computer Engineering

Q: What are the three main purposes of an operating system?
Q: List the four steps that are necessary to run a program on a completely dedicated machine.
Q: What is the main advantage of multiprogramming?
Q: What are the main differences between operating systems for mainframe computers and personal computers?
Q: In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we
Q: Define the essential properties of the following types of operating systems: a. Batch b. Interactive c. Time sharing d. Real time e. Network f. Distributed
Q: 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 forsake this principle and to “waste”
Q: Under what circumstances would a user be better off using a time-sharing system, rather than a personal computer or single-user workstation?
Q: Describe the differences between symmetric and asymmetric multiprocessing. What are three advantages and one disadvantage of multiprocessor systems?
Q: What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment?
Q: 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 the job is about to start operating on the data,
Q: How does the distinction between monitor mode and user mode function as a rudimentary form of protection (security) system?
Q: What are the differences between a trap and an interrupt? What is the use of each function?
Q: For what types of operations is DMA useful? Explain your answer.
Q: 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. Switch from user to monitor mode.
Q: Some computer systems do not provide a privileged mode of operation in hardware. Consider whether it is possible to construct a secure operating system for these computers Give arguments both that
Q: 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 operating system itself. Describe two difficulties
Q: Protecting the operating system is crucial to ensuring that the computer system operates correctly. Provision of this protection is the reason behind dual-mode operation, memory protection, and the
Q: 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 which it is caching (for instance, a cache as large
Q: Writing an operating system that can operate without interference from malicious or undebugged user programs requires some hardware assistance. Name three hardware aids for writing an operating
Q: What are the five major activities of an operating system in regard to process management?
Q: What are the three major activities of an operating system in regard to memory management?
Q: What are the three major activities of an operating system in regard to secondary-storage management?
Q: What are the five major activities of an operating system in regard to file management?
Q: What is the purpose of the command interpreter? Why is it usually separate from the kernel?
Q: List five services provided by an operating system. Explain how each provides convenience to the users. Explain also in which cases it would be impossible for user-level programs to provide these
Q: What is the purpose of system calls?
Q: 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 Section 3.3.
Q: 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 method is useful.
Q: What is the purpose of system programs?
Q: What is the main advantage of the layered approach to system design?
Q: What are the main advantages of the microkernel approach to system design?
Q: What is the main advantage for an operating-system designer of using a virtual-machine architecture? What is the main advantage for a user?
Q: Why is a just-in-time compiler useful for executing Java programs?
Q: Why is the separation of mechanism and policy a desirable property?
Q: The experimental Synthesis operating system has an assembler incorporated within the kernel. To optimize system-call performance, the kernel assembles routines within kernel space to minimize the
Q: MS-DOS provided no means of concurrent processing. Discuss three major complications that concurrent processing adds to an operating system.
Q: Describe the differences among short-term, medium-term, and long-term scheduling.
Q: 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 register sets. What else must happen if the new
Q: Describe the actions a kernel takes to context switch between processes.
Q: Provide two programming examples of multithreading giving improved performance over a single-threaded solution.
Q: Provide two programming examples of multithreading that would not improve performance over a single-threaded solution.
Q: What are two differences between user-level threads and kernel-level threads? Under what circumstances is one type better than the other?
Q: Describe the actions taken by a kernel to context switch between kernel-level threads.
Q: Describe the actions taken by a thread library to context switch between user-level threads.
Q: What resources are used when a thread is created? How do they differ from those used when a process is created?
Q: A CPU scheduling algorithm determines an order for the execution of its scheduled processes. Given n processes to be scheduled on one processor, how many possible different schedules are there? Give
Q: Define the difference between preemptive and nonpreemptive scheduling. State why strict nonpreemptive scheduling is unlikely to be used in a computer center.
Q: Consider the following set of processes, with the length of the CPU-burst time given in milliseconds:
Q: Suppose that the following processes arrive for execution at the times indicated. Each process will run the listed amount of time. In answering the questions, use nonpreemptive scheduling and base
Q: 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 putting two pointers to the same process in the ready
Q: What advantage is there in having different time-quantum sizes on different levels of a multilevel queuing system?
Q: Consider the following preemptive priority-scheduling algorithm based on dynamically changing priorities. Larger priority numbers imply higher priority. When a process is waiting for the CPU (in the
Q: Many CPU scheduling algorithms are parameterized. For example, the RR algorithm requires a parameter to indicate the time slice. Multilevel feedback queues require parameters to define the number of
Q: 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 recent past. Why will this algorithm favor
Q: Why does Solaris 2 implement multiple locking mechanisms? Under what circumstances does it use spin locks, semaphores, adaptive mutexes, conditional variables, and readers-writers locks? Why does it
Q: Explain the differences in the degree to which the following scheduling algorithms discriminate in favor of short processes: a. FCFS b. RR c. Multilevel feedback queues
Q: List three examples of deadlocks that are not related to a computer-system environment
Q: Is it possible to have a deadlock involving only one single process? Explain your answer.
Q: 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 that the system is deadlock free.
Q: 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 one at a time. Show that the system is
Q: Consider the following resource-allocation policy. Requests and releases for resources are allowed at any time. If a request for resources cannot be satisfied because the resources are not available,
Q: Explain the difference between internal and external fragmentation.
Q: Describe the following allocation algorithms: a. First fit b. Best fit c. Worst fit
Q: 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 its ability to use the CPU, but where the process
Q: 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 processes of 212K, 417K, 112K, and 426K (in order)?
Q: Why are page sizes always powers of 2?
Q: 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 logical address? b. How many bits are there in the
Q: 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 should it or should it not?
Q: 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 reference take? b. If we add associative registers, and
Q: 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 decrease the amount of time needed to copy a large
Q: Why are segmentation and paging sometimes combined into one scheme?
Q: Describe a mechanism by which one segment could belong to the address space of two different processes.
Q: Explain why it is easier to share a reentrant module using segmentation than it is to do so when pure paging is used.
Q: Consider the following segment table:
Q: 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 address into a physical address. b. What are the
Q: Under what circumstances do page faults occur? Describe the actions taken by the operating system when a page fault occurs.
Q: 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 occurring in it. For any page-replacement
Q: 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 implemented by paging, and the page size is 4096
Q: Which of the following programming techniques and structures are “good” for a demand paged environment? Which are “not good”? Explain your answers. a. Stack b. Hashed symbol table c.
Q: 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 available or the replaced page is not modified and 20
Q: Consider the following page-replacement algorithms. Rank these algorithms on a five point scale from “bad” to “perfect” according to their page-fault rate. Separate those algorithms that
Q: When virtual memory is implemented in a computing system, there are certain costs associated with the technique and certain benefits. List the costs and the benefits. Is it possible for the costs to
Q: An operating system supports a paged virtual memory, using a central processor with a cycle time of 1 microsecond. It costs an additional 1 microsecond to access a page other than the current one.
Q: Consider a demand-paging system with the following time-measured utilizations: CPU utilization 20% Paging disk 97.7% Other I/O devices 5% Which (if any) of the following will (probably)
Q: 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 following replacement algorithms, assuming one,
Q: 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 hardware does not provide one. Sketch how you could
Q: Segmentation is similar to paging but uses variable-sized “pages.” Define two segment replacement algorithms based on FIFO and LRU page-replacement schemes. Remember that since segments are not
Q: A page-replacement algorithm should minimize the number of page faults. We can do this minimization by distributing heavily used pages evenly over all of memory, rather than having them compete for a
Q: Consider a demand-paging system with a paging disk that has an average access and transfer time of 20 milliseconds. Addresses are translated through a page table in main memory, with an access time
Q: Consider a demand-paged computer system where the degree of multiprogramming is currently fixed at four. The system was recently measured to determine utilization of CPU and the paging disk. The
Q: 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 tables be set up to simulate base and limit
Q: 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?
Q: What problems arise if the directory structure is a general graph?
Q: What is garbage collection?
Q: How can we protect files on a single-user system?
Q: What might damage files?
Q: List kinds of access we might want to limit on a multi user system.
Q: List four ways systems might provide for users to protect their files against other users.
Q: 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) associated with it? The CPU also has a key (the

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