# Chp 1 Introduction
###### tags: `作業系統`

[TOC]

### Operation System

* Computer Structure


“The one program running at all times on the computer” is the kernel.

### Program, Proccese, Thread

Ref: [Program/Process/Thread 差異](https://medium.com/@totoroLiu/program-process-thread-差異-4a360c7345e5)

* **Program**: 還尚未load入記憶體的 code (工廠藍圖)
* 相同 Program 的 Process 可以多個同時存在
* Passive Entity

* **Process**: 已經執行並且 load 到記憶體中的 Program (運作之工廠)
* Active Entity
* Process 是電腦中已執行 Program 的實體
* 一個 CPU 一次只能執行一個 Process，每一個 Process 互相獨立
* Process 的運行量總量不會少於 CPU 的總量

* **Thread**: Process 是 Thread 的容器 (工廠工人)
* 同一個 Process 可以同時存在多個 Thread
* ~~同一個 Process 底下的 Thread 共享資源，不同的Process 則否~~
* 兩個以上執行緒若同時存取或改變全域變數(Global Variable)，則可能發生同步(Synchronization，恐龍本第六章)問題。
* 若執行緒之間互搶資源，則可能產生死結(Deadlock，恐龍本第七章)
>[color=#ff00ff]不同的Process一樣可以共享資源，這可以藉由share memory或是message passing model達成，message passing model可以是socket或是其他的通訊方式
>不管是thread或是process之間，要共享資源就要解決互搶資源的現象，如同Thread第3,4點所述，解決的方式可以藉由添加互斥鎖，之後會教。
>[name=Neko]

* **program counter**
* specifying location of next instruction to execute
* one program counter per thread

### Interrupt
* **Polling**
* Idle 時，固定隔一段時間從`Queue`檢查是否有`interrupt`
>[color=#ff00ff]說Queue好像有點怪怪的，但是總之就是固定去檢查裝置
>[name=Neko]
* **vectored interrupt** system
* [vectored v.s. non-vectored interrupt](https://vivadifferences.com/difference-between-vectored-and-non-vectored-interrupts/)

* Interrupt v.s Trap(or exception)
- **Interrupt**
* hardware-generated
- **Trap**:
* software-generated

### I/O Structure
* System call
- request to the OS to allow user to wait for I/O completion.

* Device-status table
- 同時有很多I/O運作，儲存各個I/O狀態在此

### Storage

* Storage Hierarchy
- Speed
- Cost
- Volatility (need extra power to store the data)


* **Main Memory**
- Random access
- Volatile
* **Caching**
- Copying information into faster storage system

* **Direct Memory Access(DMA)**
- Transfers blocks of data from buffer storage directly to main memory without CPU.
- Close to the memory speeds

### Computer-System Architecture

* **DEFINITION**
* **Core** — The basic computation unit of the CPU.
* **CPU** — The hardware that executes instructions.
* **Processor** — A physical chip that contains one or more CPUs.

* **Multiprocessors**
* parallel systems, tightly-coupled systems
* [Types & Difference](https://techdifferences.com/difference-between-symmetric-and-asymmetric-multiprocessing.html)
* Asymmetric Multiprocessor
* Only Master processor run the tasks of OS
* Master processor allocate work to slave processor
* No-shared memory
* Symmetric Multiprocessor
* Each processor run the tasks in OS
* shared memory
* **Multi-chip, Multicores**

* **Multiprocessor VS Multicore**

| | Multicore | Multiprocessor |
| -------- | -------- | -------- |
| Definition | a **single CPU** with <br> multiple execution unit | a system that <br> has **two or more CPUs** |
| Advantage | execute single program faster | execute multiple program faster |
| Reliablility | not reliable | more reliable<br>CPU won't affect the other|

* **Multiprogramming (Batch system)**
* organizes jobs to keep CPU executing
* require **job scheduling**

* **Timesharing (multitasking)**
* CPU switches jobs frequently to create **interactive** computing
* require **CPU scheduling**

* **Clustered Systems**
* multiple systems working together
* **parallelization** required
* **distributed lock manager** (DLM) avoid conflict operations
* Type
* Asymmetric
* one machine in hot-standby mode
* a hot standby node is part of the system . The hot standby node continuously monitors the server and if it fails, the hot standby node takes its place.
* Symmetric
* multiple nodes running, monitoring each other

>[color=#00ff00]Network 的概念？
>
>[name=Omnom]

### Dual-Mode
* **Purpose:** Allow OS to protect itself and other system components.
* **user mode (mode bit=1)** and **kernel mode (mode bit=0)**
* Some privileged instructions only excutable in kernel mode

### Network
* **Distributed Computing (TCP/IP)**
- Local Area Network (LAN)
- Wide Area Network (WAN)
- Metropolitan Area Network (MAN)
- Personal Area Network (PAN)

* **Client-Server**
- Compute-server: clients request services
- File-server: clients store and retrieve files

* **Peer-to-Peer**
- no distinguish clients and servers
- Broadcast request via **discovery protocol**

### Virtualization
[Simulator and Emulator](https://hwchen18546.wordpress.com/2014/03/06/vm-simulator-and-emulator/)