What is an Operating System?
An operating system is system software that directs computer hardware and software resources. It also offers common services for computer programs. Time-sharing operating systems program tasks for proficient use of the system. It might also include accounting software for cost provision of processor time, printing, mass storage and other resources.
Explain the Concept of Reentrancy.
A Reentrant procedure is one in which numerous users can share one copy of a program at the same time.
Reentrancy has 2 key aspects. The program code cannot fix itself and the local data for each user method must be stored independently. The constant part is the code and the transitory part is the pointer back to the calling program and local variables used by the program.
Each implementation instance is called activation. It executes the code in the stable part but has its own copy of local parameters/variables. The temporary part related to each instigation is the activation record. Usually the activation record is kept on the stack.
A Reentrant process can be interrupted and called by an interrupting program. It still executes correctly on returning to the procedure.
What is a Binary Semaphore? What is its Use?
A binary semaphore is one which takes 0&1 as values. They are used to synchronise concurrent processes and apply mutual exclusion.
What is Thrashing?
It is an experience in virtual memory schemes when the central processing unit changes pages rather than fulfilling instructions. This is due to an excessive number of page faults.
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What is Response Time and Turnaround Time?
Response time is the interlude between the submission of a request and the first answer to that request. Turnaround time is the interlude between the proposal of a job and its completion. List the Coffman’s Conditions That Result in a Deadlock?
1. Hold and Wait – A process may be given some resources while waiting for others. 2. No Prevention – No resource can be effectively removed from a process holding it. 3. Circular Wait – A locked chain of processes exist so each process holds at least one resource required by another process in the chain. 4. Mutual Exclusion – Only one method may use a critical resource at a time. What are Short, Long and Medium – Term Scheduling?
• Long-term scheduler defines which programs are admitted to the processing system. It manages the degree of multiprogramming. Once entered it becomes a procedure. • Medium term scheduling is part of the swapping function. This links to procedures that are in a deferred or blocked state. They are exchanged out of real-memory until they are ready to perform. The swapping-in choice is based on memory-management criteria. • The short-term scheduler also known as a dispatcher, implements most frequently and makes the finest-grained decision about which process will be executed next. This scheduler is evoked whenever an event occurs. It may result in the interruption of one process by pre-emption. What is the Working Set and Resident Set of a Process?
The Resident Set is that part of the procedure image that is actually in real-memory at a particular time. The Resident Set subset is the Working Set that is actually needed for execution. (Connect this to the variable-window size method for exchange techniques).
What is Cycle Stealing?
Cycle Stealing is met in the context of Direct Memory Access (DMA). The DMA controller can use the data bus when the CPU does not need it. Alternatively, it may power the CPU to temporarily interrupt the operation. This method is called cycle stealing which can be completed at specific break points in a directive cycle.
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