The mission/role of OS OPERATING-SYSTEM OPERATIONS

Operating-System Operations

• Driven model of operating system
• Hardware protection
• Process management
• Memory management
• Storage management
• I/O Subsystem

Interrupt driven operations

• Interrupt driven by hardware

Hardware Protection

• Prevent errors and misuse
• Dual-Mode Operations – a mode bit
  1. User mode
  2. Kernel mode

@ System call 
就像是系統提供的函式庫供使用者做些事情
每個 System call 都對應到不同代號
changes mode to kernel, return from
call resets it to user

@ API
更方便 "間接" 的操作系統
比 System call 更高一層(能夠可攜化，在不同OS使用)

Timer control

prevent infinite loop / process hogging resources

比較 :

//=========================

1. Interrupt : 避免發生例外情況
2. Timer : 預防程式長期佔有某項資源(定期call Interrupt)

//=========================

Process Management

程序執行結束回收資源
任何一個"緒"都有一個 program counter 算現在執行到哪裡了
當一個Process就能接續下一個

1. program : 被動的程序單元
2. process : 主動的程序單元

// A life cycle of process //

• Services
    • Creating and deleting both user and system processes
    • Suspending and resuming processes (ch5)
    • Providing mechanisms for process synchronization (ch6)
    • Providing mechanisms for process communication (ch4)
    • Providing mechanisms for deadlock handling (ch7)

Memory Management

CPU最遠只能管到記憶體，所以資料要先load進記憶體，
這就是Memory Management要處理的事情

• Services
    • Memory usage and availability
    • Decision of memory assignment
    • Memory allocation and de-allocation

Storage Management

OS provides a logical storage unit: File

• Services
    • File creation and deletion
    • Directory creation and deletion
    • Primitives for file and directory manipulation
    • Mapping of files onto secondary storage
    • Backing up files on stable (non-volatile) storage media

I/O Subsystem (ch13)

I/O工作範圍廣泛，所以OS於kernal另設置kernal I/O Subsystem 

buffering(緩衝器), caching, and spooling(序列緩衝器) system

spooling

User Privilege權限

鳥哥_第六章、Linux 的檔案權限與目錄配置

-rwxr--r--
user /group /other