How can you get/set an environment variable from a program?

Correct Answer: The `fork()? used to create a new process from an existing process The new process is called the child process, and the existing process is called the parent We can tell which is which by checking the return value from `fork()? The parent gets the child?s pid returned to him, but the child gets 0 returned to him

Correct Answer: We encounter cycle stealing in the context of Direct Memory Access (DMA) Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation The latter technique is called cycle stealing Note that cycle stealing can be done only at specific break points in an instruction cycle

Correct Answer: Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them CPU scheduling decisions may take place when a process: 1Switches from running to waiting state 2Switches from running to ready state 3Switches from waiting to ready 4Terminates Scheduling under 1 and 4 is non-preemptive All other scheduling is preemptive

Correct Answer: - Process management - Main memory management - File management - I/O system management - Secondary storage management - Networking - Protection system - Command interpreter system

Correct Answer: An operating system is a program that acts as an intermediary between the user and the computer hardware The purpose of an OS is to provide a convenient environment in which user can execute programs in a convenient and efficient manner It is a resource allocator responsible for allocating system resources and a control program which controls the operation of the computer hardware

Correct Answer: TRUE

Explanation:

The given statement is clearly true.

Correct Answer: Paging

Explanation:

Paging is a memory management technique in which process address space is broken into blocks of the same size called pages.

Correct Answer: Multi programming: Multiprogramming is the technique of running several programs at a time using timesharing It allows a computer to do several things at the same time Multiprogramming creates logical parallelism The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously The operating system selects a job from the job pool and starts executing a job, when that job needs to wait for any i/o operations the CPU is switched to another job So the main idea here is that the CPU is never idle Multi tasking: Multitasking is the logical extension of multiprogramming The concept of multitasking is quite similar to multiprogramming but difference is that the switching between jobs occurs so frequently that the users can interact with each program while it is running This concept is also known as time-sharing systems A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of time-shared system Multi threading: An application typically is implemented as a separate process with several threads of control In some situations a single application may be required to perform several similar tasks for example a web server accepts client requests for web pages, images, sound, and so forth A busy web server may have several of clients concurrently accessing it If the web server ran as a traditional single-threaded process, it would be able to service only one client at a time The amount of time that a client might have to wait for its request to be serviced could be enormous So it is efficient to have one process that contains multiple threads to serve the same purpose This approach would multithread the web-server process, the server would create a separate thread that would listen for client requests when a request was made rather than creating another process it would create another thread to service the request To get the advantages like responsiveness, Resource sharing economy and utilization of multiprocessor architectures multithreading concept can be used

Correct Answer: Turnaround time is the interval between the submission of a job and its completion Response time is the interval between submission of a request, and the first response to that request

Correct Answer: Free memory is maintained in linked lists, each of equal sized blocks Any such block is of size 2^k When some memory is required by a process, the block size of next higher order is chosen, and broken into two Note that the two such pieces differ in address only in their kth bit Such pieces are called buddies When any used block is freed, the OS checks to see if its buddy is also free If so, it is rejoined, and put into the original free-block linked-list