2.9 List five services provided by an operating system, and explain how each creates convenience for users. In which cases would it be impossible for user-level programs to provide these services? Explain your answer. Answer: The five services are: a. Program execution . The operating system loads the contents (or sections) of a file intomemory and begins its execution.Auser-level program could not be trusted to properly allocate CPU time. b. I/O operations .Disks, tapes, serial lines, and other devicesmust be communicated with at a very low level. The user need only specify the device and the operation to perform on it, while the system converts that request into device- or controller-specific commands. User-level programs cannot be trusted to access only devices they Practice Exercises 7 should have access to and to access them only when they are otherwise unused. c. File-system manipulation . There are many details in file creation, deletion, allocation, and naming that users should not have to perform. Blocks of disk space are used by files andmust be tracked.