操作系统 架构

操作系统的定义：

1 an intermediary between a user of a computer and the computer hardware

2 Operating system goals:
     2.1Execute user programs and make solving user problems easier.
     2.2 Make the computer system convenient to use.

3Use the computer hardware in an efficient manner.

OS is a resource allocator 资源分配器
1 Manages all resources
2Decides between conflicting requests for efficient and fair resource use
 OS is a control program  程序管理者
1 Controls execution of programs to prevent errors and improper use of the computer

管理控制程序的执行、使得计算机更使用便捷、分配计算机资源、使得计算机运行高效

计算机系统组成Computer System Structure：

1 Hardware

2Operating system

3Application programs

4Users

计算机启动：

引导程序：存储于ROM或EPROM，作用：初始化系统、加载系统内核，开始执行系统内核和相关程序

启动过程：

计算机通电-->读取ROM芯片BIOS（基本输出输入系统）程序 （硬件自检POST）-->BIOS根据启动顺序（外部储存设备的排序）  转移控制权-->读取设备扇区的主引导记录MBR（操作系统的硬盘位置）-->根据硬盘分区的卷引导记录VBR得知操作系统在分区位置-->加载操作系统

计算机系统操作 Computer-System Operation 
1 I/O devices and the CPU can execute concurrently. I/O、cpu 可以并发执行
2 Each device controller is in charge of a particular device type.
1 Each device controller has a local buffer.
2 CPU moves data from/to main memory to/from local buffers
3 I/O is from the device to local buffer of controller.
4 Device controller informs CPU that it has finished its operation by causing an interrupt.

操作系统提供的服务：

 1 One set of operating-system services provides functions that are helpful to the user（帮助用户使用计算机）

User interface（UI）：Command-Line (CLI), Graphics User Interface (GUI)

Program execution

 I/O operations

File-system manipulation

Communications

 Error detection

2Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing（提高计算机运行效率）

 Resource allocation

 Accounting

Protection and security

Three general methods used to pass parameters to the OS：

1pass the parameters in registers

2Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register

3Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system

Types of System Calls（系统调用的类型）
1 Process control
2 File management
3 Device management
4 Information maintenance
5 Communications

 System programs provide a convenient environment for program development and execution. The can be divided into（系统程序，系统程序包装了系统调用）
1 File manipulation
2 Status information
3 File modification
4 Programming language support
5 Program loading and execution
6 Communications
7 Application programs

操作系统设计和实现原则：

 User goals and System goals
1 User goals – 使用：方便使用，方便学习，安全可靠，快速

operating system should be convenient to use, easy to learn,reliable, safe, and fast
2 System goals –实现：容易设计、容易实现、容易维护、灵活安全、没有错误

 operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

Microkernel System Structure 微内核架构

 Benefits:
1 Easier to extend a microkernel 易扩展
2 Easier to port the operating system to new architectures 已变形
3 More reliable (less code is running in kernel mode) 可靠
4 More secure 安全
Detriments:
1Performance overhead of user space to kernel space communication (message passing)  用户空间与内核空间需要进行消息传递，运行效率