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11/13 11/6 OS作業
名稱	11/6 OS作業
日期	11/13
課程名稱	作業系統
指導教師	劉艾華

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?
(1)Message passing is useful for exchanging smaller amounts of data, because conflicts need be avoided. It is also easier to implement than is shared memory for inter computer communication.
(2)The advantages of message passing is memory is scalable with the number of processors. Increase the number of processors and the size of memory increases proportionately,and disadvantages is It may be difficult to map existing data structures, based on global memory, to this memory organization.
Shared memory allows maximum speed and convenience of communication, as it can be done at memory speeds when within a computer. Shared memory is usually faster than message passing, as message-passing are typically implemented using system calls and thus require the more time-consuming tasks of kernel intervention. In contrast, in shared-memory systems, system calls are required only to establish shared-memory regions.

2. What is “system calls?” Please specify the functions and the purposes of a system call in a computer system.
(1)System call provide the interface between a running program and the operating system and System call is available to the operating system used by the application function call. The purpose of system calls is allow user-level processes to request services of the operating system.

3. Please specify different ways for using the hardware configuration during the system generation (SYSGEN). What are the major differences between these different ways?
(1)Used to modify a copy of the source code of the OS and have it re-compiled. along with conditional compilation, produce an output-object version of the operating system that is tailored to the system decribed.Used to create tables and the selection modules from a precompiled library. The needed modules are linked together to form the generated OS. The selection allows the library to contain the device drivers for all supported I/O devices, but only those needed are linked into the operating system.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.

更新日期：2015/11/13 下午 08:46:56