homework -2 Version 0 |
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👤 Author: by zhangleilaogeqqcom 2019-10-31 12:50:32 |
1.describe the life circle of process
Process is a dynamic entity, from creation to extinction, is the whole life cycle of a process. Possible process
There are three kinds of states.
+ Ready state: The process has acquired all other resources except the cpu, waiting for the CPU to schedule in the ready queue
+ Execution status: the CPU has been obtained and all required resources are running
+ Blocking state (waiting state): A process abandons the processor or process book because it waits for the required resources.
To have no processor, and other resources are not satisfied.
2.why each process must have one PCB
PCB is a part of process entity and the most important record data structure in OS. It records all the information needed by OS to describe the process and control the operation of the process. The function of PCB is to make a program (including data) that can not run independently in a multi-programming environment become a basic unit that can run independently and a process that can run concurrently with other processes. In other words, OS controls and manages concurrent processes according to PCB. In the whole life of a process, the system always controls the process through PCB. That is to say, the system perceives the existence of the process according to the PCB of the process. So, PCB is the symbol of the existence of the process.