Tuesday, April 10, 2012

Scheduling the Operatng System on Windows XP SP 3

Scheduling is a collection of policies and mechanisms in the operating system associated with the sequence of the computer systems of work done. Scheduling process will be discussed here is the process of scheduling the operating system WINDOWS XP SP3.

The main goal or purpose of the scheduling process performance optimization according to certain criteria. where the optimization criteria for measuring and scheduling of work, among others

• For all the work getting a fair service (firness).
• To use a processor can be maximized.
• In order for the response time can be minimized.
• For balanced use of resources.
• Turn arround time, the time since the program entered the system until the process is complete.
• Efficient, the process remains in busy state is not idle.
• For breakthrough (thoughput) can be maximized.
There are three types of schedulers are together in a complex operating system, namely:

A. Short-term scheduler (Scheduler short term)
Charge of scheduling processor allocation among ready processes in main memory scheduling run every event of a transfer process to select the next process to run.
B. Medium-term scheduler (medium term Scheduler)
After the execution for a time, may postpone an execution process for making a service request inputs / outputs or invoke a system call. Delayed processes can not make any progress toward completion until the conditions that lead to delayed removed. So that memory space can be beneficial, then the process was transferred from main memory to secondary memory to make room for other processes. Main memory capacity is limited to a number of active processes. Activities pending the transfer process from the main memory to secondary memory is called swapping. Processes have little interest at that time as a delayed process. However, once the conditions that make it disappear delayed and put back into main memory and ready.
C. Long-term scheduler (Scheduler long term)
Scheduler is working on a batch queue and select the next batch to be executed. Batch processes usually are with the intensive use of resources (ie processing time, memory, input / output), these programs are a low priority, is used as a filler (for processors busy) during periods of activity of low job-interactive job.

Windows XP uses an algorithm, priority-based scheduling quantum reemptive based priority scheduling.
Picture Process In Windows Xp Threads are scheduled in the process, Because preemptive priority algorithm is implemented with a queue, may be considered as multiple feedback-queue algorithm. However, each Threads are usually limited to small groups of 5 levels of priority, Preemption can occur due to one of four reasons:
o higher priority thread becomes ready
o thread ends
o quantum expires
o thread blocking system calls, such as for I / O, in this case left the state ready to be a state of waiting.
Quatum picture in windows XP 32 priority levels are used, where the priority 31 is the highest priority and priority 0 is the lowest priority :
o memory management thread: priority 0
o variable priority class (1-15)
o real-time priority class (16-31)
o Threads in real-time class has remained the priority.
o Threads that run is always the highest priority.
o If no thread is ready, Threads idle run.
o When the time quantum the thread runs out, the priority is lowered, but the priority is never lowered too far.
When Threads be ready after a wait state, it is given the highest priority of any threads of the process associated with the current program using the user is given more priority.