操作系统英文版

Introduction to Operating Systems(Spring 2001)Final Exam SolutionsNote: There are 17 questions, one of which is extra credit. Each question is worth 10 points.1. Early Intel processors such as the 8086 did not support dual-mode operation (user and supervisor modes). This had a fairly major impact on the type of system that could be implemented on these processors, and most did not support multi-user operation. Discuss a few potential problems that could arise in trying to support multi-user operation on such a system.There are many problems with multi-user operation on such a system. In effect, everything that we protect in modern operation systems is unprotected. This means that:∙Memory is unprotected. A process could read or overwrite another process memory. A process could also read or overwrite the kernel'smemory.∙Timers are unprotected. A process could change the timers arbitrarily and mess up other processes execution or run as long as it wanted.∙Devices are unprotected. A process could arbitrarily access devices, messing up permanent storage, interfering with other processes' useof the devices, etc.∙Special instructions are unprotected. Any process could halt the machine or cause other problematic operations to execute.∙Etc.2. What are the differences between traps and interrupts? What is the use of each?Traps and interrupts are both methods for calling operating system functions by non-operating system entities. The difference is what entity does thecalling, and how the "call" is done. Traps allow user programs to call OS functions by calling a special trap instruction. Interrupts allow devices to "call" operating system functions by raising a signal on a special hardware bus. They also differ in terms of how the "parameters" are passed, and in terms of what operations are supported by each.3. What is a process? What information does an operating system generally need to keep about running processes in order to execute them?A process is an executing program.An operating system needs to know a number of things about each running program:∙Process name∙Address translation information (e.g., page table)∙Program counter∙Register values∙Process Status∙Recent past behaviour (for scheduling)∙...4. Memory management is important in operating systems. Discuss the main problems that can occur if memory is managed poorly.Many problems can occur if memory is managed poorly:∙Poor performance (i.e., lots of paging)∙Thrashing∙Protection violations (i.e., multiple processes accessing the same page)∙...5. What are the five major activities of an operating system in regard to file management? Why is the file interface used in many modern systems to interact with devices as well as files?1.Create2.Open3.Close4.Read5.Write6.DeleteHmmm, I guess there are really 6. Many people talked about different aspects, and I looked in the book (chapter 3 or 4, I don't have it in front of me right now) and found a discussion that was somewhat different - it talked about file management, storage management, directories, etc. So, any combination of these will get full credit.The file interface is used in many modern systems to interact with devices as well as files because it provides a simple abstraction for device interaction: open a connection to the device, read or write from/to it, close the connection. This interface also provides uniform and simple naming and protection mechanisms.6. User-level threads are threads that are scheduled directly by the process they are part of rather than by the kernel - the kernel schedules the processes, and any process that has threads schedules them however it wants within its time slice. Describe briefly how such a scheme would work. Can you think of any problems with such an implementation? Each process would have to keep track of the threads to be executed. It would have to allocated stack space for each one. It would have to have a program counter and stack pointer for each one. It would also have to manage the registers associated with these values, filling in the appropriate values for the thread it wants to execute. Finally, it will need to have a timer (provided by the OS) to wake up the scheduler thread, and that thread will do context switching among the other threads as appropriate.Possible problems include:Scheduling difficulties: Scheduling is not a trivial thing to program.Having user。