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# System prepended metadata

title: 作業系統筆記(台科資管 賴教授)

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# 作業系統筆記(台科資管 賴教授)
* **After I/O starts, control returns to user** program without waiting for I/O completion
    * **System call** – request to the OS to allow user to wait for I/O completion
    * **Device-status table** contains entry for each I/O device indicating its type, address, and state
    * OS indexes into I/O device table to determine device status and to modify table entry to include interrupt

* Only one interrupt is generated per block, rather than the one interrupt per byte

* Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage

* **Multiprocessors systems** growing in use and importance
Also known as **parallel systems**, **tightly-coupled systems(vs. loosely-coupled 透過網路的分散式運算系統)**
Advantages include:
    * Increased throughput
    * Economy of scale(規模效益)
    * Increased reliability – graceful degradation(?降解) or fault tolerance
* Two types:
    * Asymmetric Multiprocessing(不對稱，有一個manager cpu，通常是超級電腦)
    * Symmetric Multiprocessing(無manager cpu)





