# 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)

* 多核心
* **UMA** and **NUMA** architecture variations

* Clustered Systems
* Like multiprocessor systems, but multiple systems working together

* **Asymmetric(非對稱) clustering** has one machine in hot-standby mode, **one monitoring others**
* Symmetric clustering has multiple nodes running applications, monitoring each other

* Operating System Structure
* Multiprogramming
* many user
* One job selected and run via job scheduling
* When it has to wait (for I/O for example), OS switches to another job
* Timesharing(multitasking) : CPU switches jobs so frequently
* 在memory裡面的是process
* If several jobs ready to run at the same time => CPU scheduling

* Interrupt driven by hardware
* Software error or request creates exception or trap
* Division by zero, request for operating system service

* Process Management
* Single-threaded process has one program counter specifying location of next instruction to execute
* Multi-threaded process has one program counter per thread

* 多作業系統
* Emulation
* When computer language not compiled to native code – **Interpretation**
* Virtualization－vertual machine manager(**VMM**)
* 

# CH2
* Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register
* This approach taken by Linux and Solaris

# CH3
## Communications in Client-Server Systems
* Socket
* Connection-oriented (TCP)
* Connectionless (UDP)
* MulticastSocket class– data can be sent to multiple recipients
Consider this “Date” server:

* Remote Procedure Calls(RPC)
* **Stubs**(存根、樹根、票根、菸蒂根) – client-side proxy for the actual procedure on the server
* On Windows, stub code compile from specification written in **Microsoft Interface Definition Language (MIDL)**
* Data representation handled via **External Data Representation (XDL)** format to account for different architectures
* Big-endian大字序(從高位元組開始放)
* little-endian小字序(從低位元組開始放)

# CH4
* user thread
* explicit(要在程式裡面自己new thread)
* implicit(不用自己new thread，compilers and run-time libraries幫你做到)