The operating system is responsible for several other aspects of disk management, too. Disk Formatting A new magnetic disk is a blank slate: It is just platters of a magnetic recording material. Before a disk can store data, it must be divided into sectors that the disk controller can read and write...
C-SCAN Scheduling Disk arm moves unidirectionally across the disk surface toward the inner track. When there are no more requests for service ahead of the arm, it jumps back to service the request nearest the outer track and proceeds inward again. It eliminates the discrimination of earlier strategies...
SCAN Scheduling: To overcome the high variance in response time in the SSTF method, this method is devised. It operates similar to SSTF scheduling except that initially the request with shortest seek distance is preferred, that direction is the preferred direction. If the preferred direction is outward...
First Come First Served Scheduling In this algorithm, the request which arrived first is the first to be served. There is no reordering of the queue. Once the request has arrived, its place in the schedule is fixed. The place of the request cannot be displaced due to the arrival of higher priority request...
In multiprogrammed system, many processes try to read or write the records on disks at the same time. When the requests are made faster, they are serviced either by the moving-head disks, waiting lines or queues build up for each device. In some system, the requests are serviced by simple first-in-first...
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Real-Time Scheduling Real-time computing is divided into two types. Hard real-time systems are required to complete a critical task within a guaranteed amount of time. Generally, a process is submitted along with a statement of the amount of time in which it needs to complete or perform I/O. The scheduler...
Multilevel Feedback Queue Scheduling Multilevel feedback queue scheduling allows a process to move between queues. The idea is to separate processes with different CPU-burst characteristics. If a process uses too much CPU time, it will be moved to a lower-priority queue. This scheme leaves I/O-bound...
Round Robin Scheduling In round robin scheduling processes are dispatched FIFO but are given a limited amount of CPU time called a time-slice or a quantum. If a process does not complete before its CPU time expires, the CPU is preempted and given to the next waiting process. The preempted process is...
Basic concepts The assignment of physical processors to processes allows processes to accomplish work. That assignment is a complex problem handled by the operating system. When more than one process is runable, the operating system that makes this decision is called the scheduler. The algorithm it uses...
