What OS do

操作系统是管理计算机硬件的程序

computer system: hardware, operating system, application programs, users

​ hardware: CPU, memory, I/O devices

user view

services provided by OS:

• program development (editors and debuggers)

• program execution

• access to IO devices

• controlled access to files

• system access

• error detection and response

  • internal and external hardware errors

    memory error, device failure

  • software errors

    arithmetic overflow, accesss forbidden memory locations

  外中断: interruption 与当前运行程序无关的事件

  内中断: exception / trap 非法操作码，地址越界，算术溢出，缺页，专门陷入指令…

• accounting

  • collect statistics
  • monitor performance

system view

resource allocator, control program

defining OS

kernel, one program running at all times

系统软件。程序模块的集合。组织和管理计算机的软硬件资源。

computer-system organization

computer startup: bootsrap program: stored in ROM/EEPROM, AKA firmware

硬件&固件：

​ A hardware has a physical entity

​ A hardware needs a program to run. A firmware is a program itself.

​ A hardware cannot operate without a firmware. A firmware operates on a hardware.

OS starts executing the first process, and waits for some event to occur:

• an interrupt from the hardware

  sending a signal to CPU by way of the system bus

• an interrupt from the software

  executing a system call

computer-system operation

device controller informs CPU that it has finishd its operation by causing an interrupt

interrupt:

​ interrupt vector(中断向量): the staring address of all the interrupt service routines(中断服务程序).

a trap is a software-generated interrupt caused either by an error or a user request

OS is interrupt-driven

storage structure

storage hierarchy

​ speed, cost, volatility

IO structure

• programmed IO

  IO module performs the action

• interrupt-driven IO

  processor is interrupted when IO module ready to exchange data

  processor is free to do other work

  consume a lot of processor time

  we need system call & device-status table

  • synchronous IO

    After I/O starts, control returns to user program only upon I/O completion.

  • asychronous IO

• DMA

  Transfers a block of data directly to / from memory.

  device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention.

  Only one interrupt is generated per block. The processor is only involved at the beginning and the end of the transfer.

• IO channel

  

一个CPU和多个device controller通过总线连接。每个dvice controller可负责多个特定类型设备。

OS为每个device controller提供一个device driver, driver presents a uniform interface to the device

computer-system architecture

single-processor system

multiprocessor system / parallel system / tightly coupled

增加吞吐量、规模经济、增加可靠性

graceful degradation: 提供与正常工作的硬件成正比服务的能力

fault tolerant: 超出适度退化的能力 容错

• asymmetric multiprocessing

  主从

  each processor is assigned a specific task. a master processor controls the system, allocates work to the slave processors.

• symmetric multiprocessing SMP

• multicore-CPUs

  Multiple compute cores on a single chip 多个内核 单个芯片

• blade servers 刀片服务器

  每个刀片处理器独立启动并运行各自的OS

clustered system

与多处理器系统不同：多个独立系统耦合

共享存储并通过LAN/更快内部连接

asymmetric clustering: one machine is in hot-stand-by mode(热备份)

symmetric clustering: monitor each other

OS structure

• time-sharing system(multitasking)

  interactive

  response time short

  允许多用户同时共享计算机

  CPU scheduling & multiprogramming : 以提供用户分时计算机的一部分

  为保证合理响应时间，通过swapping得到，使用virtual memory

OS operations

dual mode: user mode & monitor mode

mode bit provided by hardware

Some instructions are designated as privileged, only executable in kernel mode.

System call changes mode to kernel mode, return from call resets it to user mode.

特权指令包括转换到用户模式，IO控制，定时器管理，中断管理等

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.

memory management

determines what is in memory

Central to the operation of a modern computer system.  All data should be in memory before and after processing.  All instructions should be in memory in order to execute.

virtual memory:

storage management

• file-system management

  Access control on most systems to determine who can access what.

• mass-storage management

  secondary storage, tertiary storage

• caching

  copying information into faster storage system

  • disk cache

    A portion of main memory used as a buffer to temporarily to hold data for the disk.

  • cache memory 高速缓存

    invisible to OS

  coherency & consistency

• IO subsystem

  

protection and security

• protection

  控制进程或用户对计算机系统资源的访问的机制

• security

  防止系统不受外部或内部攻击

• access control

• information flow control

• certification

保护和安全需要系统能区分用户，user ID(UID); 需要区分用户集，group ID

privilege escalation: 有时用户需要升级特权来获取对一个活动的额外特权

distributed systems

loosely coupled

network: communication path TCP/IP协议常用

network operating system: 更自治 提供信息交换的通信 file sharing, communication, runs independently

分布式系统更少自治，不同的草作系统紧密连接，好像是一个操作系统控制网络 process migration

special-purpose systems

• real-time system

  Often used as a control device in a dedicated application

  hard/soft

• real-time embedded system 实时嵌入式系统

  OS很limited

• multimedia system 多媒体系统

  将多媒体数据加入到计算机系统(audio and video files)

• handheld system 手持系统

  PDA: personal digital assistants 专门的嵌入式系统

computing environments

traditional computing

client-server computing: computer-server, file-server

peer-to-peer computing: centralized lookupservice, discovery protocol, voice over IP

cloud computing

Operating System Concepts 7th edition

Operating System Concepts 7th edition

Operating System Concepts 7th

最后修改于 2020-02-28