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11/08 11/6 OS作業
名稱	11/6 OS作業
描述	11/6 OS作業
日期	11/08
課程名稱	作業系統
指導教師	劉艾華

1-1.
Message passing is useful when smaller numbers of data need to be exchanged, because no conflicts need to be avoided.
1-2
․Advantages of the Shared Memory Model: Conventional wisdom in the multiprocessor research community is that it is important to support a shared-address space or shared-memory communication model.
․Disadvantages of Shared Memory: One of the deficiencies of the shared-memory communication model is the fact that it is, by nature, a polling interface. While this can make for extremely efficient communication under some circumstances, it can have a negative impact on synchronization operations. This has been enough of a concern that many multiprocessor architects have augmented the basic shared-memory communication model with additional synchronization mechanisms. Another disadvantage of shared memory is that every “real” communication operation (i.e. one that causes data to cross the network) requires a complete network round-trip; no one-way communication of data is possible.
․Advantages of the Message Passing Model: One of the biggest semantic advantages of the message-passing communication model is the fact that it is, by nature, interrupt driven. Messages combine both data and synchronization in a single unit. Furthermore, the efficiency of this combination can easily be maintained by simple implementations – we shall see this in later chapters of this thesis. In this section, we want to distinguish those applications of message passing that are natural from a programmers perspective from those that represent the result of automatic code generation in support of other communication models, e.g. shared memory.
․Disadvantages of Message Passing: In addition to requiring the explicit management of data and communication, the message passing paradigm has one intrinsic disadvantage that can be mitigated but not eliminated by good interface design: the presence of higher endpoint costs in message passing models as compared to shared memory. The cost of assembling and disassembling messages, often called marshaling cost, is intrinsic to message passing because messages are, by nature, transient and unassociated with computational data structures.

2.
system call is how a program requests a service from an operating system's kernel.
Application developers often do not have direct access to the system calls, but can access them through an application programming interface (API). The functions that are included in the API invoke the actual system calls. By using the API, certain benefits can be gained:․Portability: as long a system supports an API, any program using that API can compile and run.․Ease of Use: using the API can be significantly easier then using the actual system call.

3-1
Used to modify a copy of the source code for 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.
3-2
The size and generality of the generated system and the ease of modification as the hardware configuration changes.

更新日期：2015/11/12 下午 10:17:06