ACKNOWLEGMENT
I mohd sharique ansari of B tech-M Tech (CSE) would like to thank my teacher of numerical analysis Mr. RK Gupta who helped me throughout the development of this paper in best possible way. I would like appreciate the dedication and sincerity of my teacher for his guidance without whom this paper would not been possible.
At last I would like to thank all my friends for their support.
INTRODUCTION
CPU SCHEDULING:
Scheduling basically deals with the selection of a process that exists in the memory and ready to execute. The selected process is allocated with the CPU. This function is performed by the CPU scheduler. The CPU scheduler makes a sequence of “moves” that determines the interleaving of threads.
The scheduler's moves are dictated by a scheduling policy.
A general overview of the scheduling is depicted by the below representation:
Windows process scheduling
1) Windows 3.1 xs used a non-preemptive scheduler, meaning that it did not interrupt programs. It relied on the program to end or tell the OS that it didn't need processor so that it could move on to another process. This is usually called cooperative multitasking. Windows 95 introduced a rudimentary preemptive scheduler; however, for legacy support opted to let 16 bit applications run without preemption
2) NT-based versions of Windows use a CPU scheduler based on a multilevel feedback queue, with 32 priority levels defined. It is intended to meet the following design requirements for multimode systems:
All processes receive a priority boost after a wait event, but processes that have experienced a keyboard I/O wait get a larger boost than those that have experienced a disk I/O wait.
“Foreground” processes given higher priority.
3) Windows XP uses a quantum-based, preemptive priority scheduling algorithm. The scheduler was modified in Windows Vista to use the cycle counter register of modern processors to keep track of exactly how many CPU cycles a thread has executed, rather than just using an interval-timer interrupt routine.
Linux Process Scheduling
From versions 2.6 to 2.6.23, the kernel used an O (1) scheduler. The Completely Fair Scheduler is the name of a task scheduler which was merged into the 2.6.23 release of the Linux kernel. It handles CPU resource allocation for executing processes, and aims to maximize overall CPU utilization while maximizing interactive performance. It uses that uses red-black trees instead of queues.
Two classes of processes:
Normal process scheduling uses a prioritized, preemptive, credit-based policy:
The Round Robin and FIFO scheduling algorithms are used to switch between real-time processes
Windows is by far the most popular proprietary personal computer operating system, while Linux is the most prominent free software operating system.
