# OS Chapter1 ###### tags: `作業系統` ## *Computer System Structure* :::success 1. Users 2. Aplication programs 3. Operating System - controls and coordinates use of hardware among applications and users - acting as a intermediary between a user and hardware. 4. Hardware ::: :::info ![](https://i.imgur.com/iysQ3a3.png) ::: ## *What OS do* :::success :arrow_forward:OS is a resource allocator(分配) and control program ::: ## *Operation System Definition* :::success - **kernel** : 處理軟體I/O，將這些要求**轉譯**為指令並交由中央處理器（CPU）處理 - middleware : a set of software frameworks that provide addition services to application developers. ::: ## *Computer System Organization* :::success CPU , device controllers connect through bus / hub providing access to shared memory ![](https://i.imgur.com/ezE4V73.png) ::: :::info **Clustered System** sharing storage via storage-area network(SAN) - example : 光纖、磁碟陣列 ::: ## *Computer-System Operation* :::success - 每一個device controller類型都有對應的os device driver去管理 - device controller透過interrupt(trap)告知CPU已完成工作(operation) ::: ## *Common functions of interrputs* :::success - an os is interrupt driven - 每一個硬體都有自己的**interrupt service routine(ISR)** , 當中斷產生之後控制權會交由ISR，再透過interrupt vector可以得知中斷後要往哪邊做什麼事 - two software-generated interrupt : 1. **trap** : 向系統請求的 (e.g. device controller已完成任務，透過trap告知CPU已完成) 2. **exception** : 意外(也是最常處理的) (e.g. 除以0) ::: ## *Interrupt Handling* :::success 當interrupt發生的時候，CPU將被打斷的狀況儲存在暫存器或program counter中 ::: :::info determines which type of interrupt has occurred : 1. polling interrupt system 2. vectored interrupt system ::: ## *I/O sturcture* :::success After I/O starts , control return to user program only upon I/O completion. e.g. wait loop ::: :::info After I/O starts , control returns to user program without waiting for I/O completion. - **System call** : request to 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. ::: ## *Storage structure* :::success *Main memory* - definition : only large storage media that CPU can access directly - 特色 : - random access - volatile - 舉例 : - random-access memory in the form of Dynamic Random-access Memory(DRAM) ::: :::info *Secondary storage* - definition extension of main memory that provide large nonvolatile storage capacity - 舉例 : - Hard Disk Drives(HDD) - Non-volatile memory(NVM) ::: :::warning ![](https://i.imgur.com/Y6ibZek.png) ::: ## *How a modern computer works* :::success ![](https://i.imgur.com/KH8Gogb.png) :skull: instuction execution : instruction fetch :skull: data movement : load & stall :skull: **Direct Memory Access(DMA)** : 直接傳送資料到memory不需要CPU介入 ::: ## *Computer-System Architecture* :::success *Single general-purpose processor* :arrow_forward: most systems using :arrow_forward: using bus ::: :::info *Multiprocessors* :arrow_forward: parallel systems , tightly-coupled systems :arrow_forward: using bus - 優點 : - Increased throughput - Economy of scale - increased reliability - type 1. Asymmetric Multiprocessing : each processor is assigned a special task 2. Symmetric Multiprocessing : each processor performs all tasks ::: :::warning *Clustered System* :arrow_forward: multiple systems works together , sharing storage via storage-area network(SAN) - 優點 : - provides a high-availability service - type : - Asymmetric clustering : has one machine in hot-stanby mode (透過熱備份，避免電線過熱等原因而使工作中斷) - Symmetric clustering : multiple nodes running applications , monitoring each other ::: ## *Operating-System Operation* :::success - firmware(韌體) : 初始各方面的系統，載入OS kernel及開始執行 - kernel載入 :arrow_right: start system daemons(系統服務) ::: ## *Multiprogramming and Multitasking* :::success *Multiprogramming* - batch system(批次執行) - one job selected and run via job scheduling - When it has to wait(e.g. I/O) , OS switches to another job - 要主動退出工作權才會交換 ::: :::info *Timesharing (Multitasking)* - if several jobs ready to run at the same time :arrow_right: CPU scheduling - if processes don't fit in memory , swapping moves them in and out to run - Virtual memory allows execution of process not fit completely in memory ::: ## *Dual-mode* :::success - 優點 : allows OS to protect itself and other system components - User mode and kernel mode - mode bit - 由硬體提供，用於判斷現在是user mode還是kernel mode - 有些指令被設為特權，只有kernel mode的時候可以使用 - using system call to change user mode to kernel mode , return from call resets it to user ::: ## *Protection and Security* :::success *Privilege escalation* - 優點 : 允許使用者能變更更有權限的帳號 ::: ## *Virtualization* :::success - definition : allows OS to run application within other OSes - Emulation : used when source CPU type different from target type - type - machine-level virtualization - provides virtualization services - e.g. VMM , Hypervisor - Operating-system-level virtualization - containerization :::