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11/12 os 作業 11/12
名稱	os 作業 11/12
日期	11/12

1. Which situation is suitable to use message passing instead of shared-memory model for communication between processes? What are the pros and cons of using these two models?

message passing model is more suitable to use when you are doing something more simple , and protect data from being edited by other who shouldn’t access the file.
Sharing model can simulate the message passing model , but vice versa, it does not work, Shared memory model has a disadvantage that the data or value might be changed by other process due to the sharing concept, they may be using the same source , but when we run a process to change value, the program which uses that value will all receive the changed value when they execute the program , which may end up messing up the whole system.
message passing model has the concept of sending message to others , so other will receive maybe value or data by coping it instead of sharing it , so that things won’t be messed up .


2. What is “system calls?” Please specify the functions and the purposes of a system call in a computer system.
A system call is how a program requests a service from an operating system's kernel.
System calls allow user-level processes to request services of the operating system.
System calls provide an essential interface between a process and the operating system. By doing system call , the computer will interrupt and be switched into kernel mode to either create a new process or do a hardware related service .

3. Please specify different ways for using the hardware configuration during the system generation (SYSGEN). What are the major differences between these different ways?
modify a copy of the source code of the operation system
creation of tables and the selection of modules from a precompiled library .
construct a system that is completely table driven .

更新日期：2015/11/12 下午 08:35:36