1.
-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.
-Shared-memory 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.
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.
Hardware configuration information can be used in several ways:
Used to modify a copy of the source code of the OS and have it re-compiled.
Used to create tables and modules from a precompiled library. The needed modules are linked together to form the generated OS.
Construct a system that is completely table driven. All the code is always part of the system, and selection occurs at execution time.
The size and generality of the generated system and the ease of modification as the hardware configuration changes.