Please explain in good detail

1. In a multiprogramming and time-sharing environment, several uses share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we ensure the same degree of security in a time-shared machine as in a dedicated machine? Explain your answer. 2. What is the main difficulty that a programmer must overcome in writing an operating system for a real-time environment? 3. Which of the following instructions should be privileged? a. Set value of timer. b. Read the clock c. Clear memory d. Issue a trap instruction e. Turn off interrupts. f. Modify entries in device-status table. g. Switch from user to kernel mode. h. Access I/O device. 4. 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 as a disk), why not make it that large and eliminate the device? 5. Describe some of the challenges of designing operating systems for mobile devices compared with designing operation systems for traditional PCs