21. 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 Services. PROGRAM EXECUTION: The operating system loads the contents (or sections) of a file into memory and begins its execution. A user-level program could not be trusted to properly allocate CPU time. I/O OPERATIONS: Disks, tapes, serial lines, and other devices must 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 only access devices they should have access to, and to only access them when they are otherwise unused. 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 ...
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