Operating System Series 1.2

Operating System Series

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System calls

Note: functional point of view

• a. First, with regard to process management and control
• b. Second, regarding the external device input / output
• c. The third is about the disk file management
• d. Fourth, information about access to the system
• e. Fifth, regarding the storage and release of the application

Note: in the form of angle

• System call and the general process of the operating system calls (subroutine calls) are similar, but they have a clear distinction

Job Management

1. When a job is submitted to the system, the system to open up a job control block JCB, in order to record information on the job at any time

2. Admitted operating system, in the absence of operational, called the back-up job. These jobs are stored in the auxiliary memory, by their JCB joined together to form a so-called backup job queue

3. Job scheduling: according to certain rules, choose from the backup job enters the job queue memory, competing processor, a process called job scheduling

4. Job status:

• . A state of submission: Go to secondary storage, information operations have not all entered the system, the system has not been established JCB for it, aware of its existence
• b standby state: established JCB, and discharged to the backup job queue JCB
• c. Run state :( blocking, running, ready) belong to the state run
• . D completion state: is a state of temporary

Scheduling Algorithm jobs

• . A first-come, first-served: the backup job queue to enter the job priorities turnaround time = completion time - Arrival Time

Note: If you allocate a certain memory, and does not allow the job in memory while moving, to consider the share memory size

• . B short operating priority: the minimum time required to pick and CPU resources can be satisfied from the backup job in the job queue

Note: If all the jobs "simultaneously" to reach the reserve job queue, then the use of short job first job scheduling algorithm will always get the smallest average turnaround time

• . C ratio with priority in response to: scheduling in response to the response ratio = ratio has latency / CPU time required

Attention to the problem when determining job scheduling algorithm:

• a. fair treatment of backup job queue every job, avoid doing a job for no reason or delayed indefinitely, so that all types of users satisfied

• b. enter the memory of the more than one job, a balanced use of resources in the system to avoid the use of some resources are not working, and some resources but was more competition for jobs, "busy" uneven situation

• c. and strive to serve as many jobs per unit of time, to improve the throughput of the entire system