操作系统第二章笔记---计算机系统结构
本文内容整理自西安交通大学软件学院田丽华老师的课件,仅供学习使用,请勿转载
操作系统系列笔记汇总：操作系统笔记及思维导图汇总附复习建议_Qlz的博客-CSDN博客
文章目录
文章目录
- 文章目录
- 思维导图
- Computer System Operation
- 中断机制
- 分类
- 目的
- 功能
- I/O Structure
- I/O Interrupts
- synchronous I/O
- DMA structure
- Storage Structure
- Main Memory
- Secondary Storage
- cache
- coherency and consistency (一致性)
- Storage Hierarchy(存储层次)
- Hardware Protection(硬件保护)
- Introduce
- 可以进行的保护操作
- Dual-Mode Operation(两状态操作)
- I/O Protection
- Memory Protection
- CPU protection
- The timer(定时器)
思维导图
计算机系统结构思维导图
Computer System Operation
计算机体系结构 Computer-System Architecture
- I/O devices and the CPU can execute concurrently.
I/O 设备与CPU可并行运行 - Each device controller is in charge of a particular device type.
每一设备控制器负责一个设备类型 - Each device controller has a local buffer.
每一设备控制器有一局部缓存 - CPU moves data from/to main memory to/from local buffers
CPU 通过局部缓存与主存交换数据 - I/O is from the device to local buffer of controller.
I/O从设备到设备控制器的局部缓存 - Device controller informs CPU that it has finished its operation by causing an interrupt.
设备控制器通过引起中断通知CPU操作已完成
中断机制
分类
- hardware interrupt 硬件中断
- device controller informs CPU that it has finished its operation by causing an interrupt
- disk, timer, etc.
- device controller informs CPU that it has finished its operation by causing an interrupt
- **software interrupt (trap) ** 软件中断（陷阱）
- a trap (or an exception异常)
- division by zero, invalid memory access
- a system call 系统调用(also called a monitor call)
- read( ), write( )
- a trap (or an exception异常)
目的
make the system more efficient and meanwhile more responsive
功能
a modern operating system is interrupt driven
现代操作系统是中断驱动的
interrupt transfers control to the interrupt service routine (interrupt handler) generally
中断将控制权转移到中断服务程序- separate segments of code determine what action should be taken for each type of interrupt 不同类型的中断将要执行的操作不一样
- a generic routine to examine the interrupt information, and in turn call the specific handler 有一个程序用来检验终端的类型,然后调用对应的程序
- through the interrupt vector (中断向量表), which contains the addresses of all the service routines
- e.g. MS-DOS, UNIX
中断向量是中断服务程序的入口地址
I/O Structure
peripheral(外围) device(s) attached to device controller设备与设备控制器相连
a device controller (hardware)
- local buffer storage 本地缓冲器
- a set of registers 一组寄存器
device driver, usually a software program embedded into an OS设备驱动程序
I/O Interrupts
two ways of an I/O operation 两种I/O操作
- Synchronous 同步
- Asynchronous异步
synchronous I/O mode: after I/O starts, control returns to user program only upon I/O completion 等待I/O完成后继续接下来的操作
asynchronous I/O mode: after I/O starts, control returns to user program without waiting for I/O completion 不等待I/O完成继续进行接下来的操作
- the user program will be notified about the I/O completion on a later time
- Windows message, or call back function
- the user program will be notified about the I/O completion on a later time
synchronous I/O
- busy wait method 忙等方式
- wait instruction idles(空转) the CPU until the next interrupt
- wait loop (contention for memory access)
- Loop: jmp Loop
- drawbacks: at most one I/O request is outstanding at a time, no simultaneous I/O processing 每次只能有一个I/O请求,没有同时的I/O处理
- interrupt based method: multiple I/O 中断方式
- device-status table contains entry for each I/O device indicating its type, address, and state
- a wait queue (a list of waiting requests) for each I/O device
DMA structure
DMA:Direct Memory Access
low speed device like a typical terminal input device(典型输入终端设备) leaves most CPU time for other operations 在发出I/O请求后CPU正常运行,当运行完成后产生中断通知CPU,CPU处理中断完成后继续正常运行
- usually assigned a low interrupt priority, allowing other more important interrupts to be processed first 低中断优先级
high-speed I/O devices able to transmit information at close to memory speeds
- if the CPU needs to respond to each interrupt for every byte, it does not have much time for process execution 每次发出I/O请求都相应会浪费资源,会等很多一起响应
DMA - device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention设备控制器在本地缓冲和内存之间直接传输一整块数据而无需CPU干预
- setting up buffers, pointers, and counters
- only one interrupt is generated per block, rather than the one interrupt per byte
DMA controller steals memory cycles from CPU DMA控制器从CPU中窃取内存周期
Storage Structure
- Storage systems organized in hierarchy.存储系统分层组织
- Speed 速度
- cost 成本
- volatility 易失性
Main Memory
- random access memory (RAM, DRAM)
- main memory are the only large storage that the CPU can access directly CPU可以直接访问的唯一大型存储介质
- store data and instructions
- problems with RAM
- not big enough, too small to store all programs and data needed permanently 不够大
- volatile(易失性), contents lost when power is turned off
Secondary Storage
- extension of main memory主存的扩展
- big enough
- non-volatile, permanent 提供了非易失的存储容量
- magnetic disk 磁盘-覆盖了磁记录材料的硬金属或玻璃盘片
- random access (随机存取)
- magnetic tape 磁带
- sequential access (顺序存取)
- floppy disks (软盘), CD-ROMs, etc.
- data exchange (small and light, easy to carry)
cache
- use of high-speed memory to hold recently-accessed data 使用高速存储保存近期访问的数据
- cache (built into CPU)
- data cache
- instruction cache, code cache
- cache management
- locality
- above 80% hit ratio(命中率)
- caching introduces another level in storage hierarchy, and it requires data that is simultaneously(同时) stored in more than one level to be consistent(保持一致)
coherency and consistency (一致性)
- the copy of a datum(数据) appears in many levels of storage hierarchy
- single process, easy 单道程序,正常
- multiprogramming environment
- multiprocessor environment
- cache coherency, handled by hardware
- distributed environment
Storage Hierarchy(存储层次)
- Caching – copying information into faster storage system; 缓存- 把信息复制进较快的存储系统；
- main memory can be viewed as a last cache for secondary storage. 主存可看作为二级存储器的最后一个缓存
Hardware Protection(硬件保护)
Introduce
- single-user programmer-operated system, complete control of the computer system, no protection 单用户系统，程序员可完全控制系统
- early OS, called resident monitor, still no protection 早期OS称为常驻监督程序，没有保护
- batch system, need some protection
- e.g. an indefinite loop reading cards不断读取卡片
- multiprogramming, a program may accidentally or deliberately/maliciously modify the code or data of another program
- multi-user environment, need protection for files, data on disk/tape 多用户环境，需要保护磁盘上的文件、数据
- hardware trap to the OS, 硬件陷入到OS ; when
- illegal instructions, or access memory not in the address space, etc.非法指令，或访问不属于自己的地址空间的内存
- process terminated/aborted, core dumped 进程终止
可以进行的保护操作
- Dual-Mode Operation 两状态操作
- I/O Protection I/O保护
- Memory Protection 内存保护
- CPU Protection CPU 保护
Dual-Mode Operation(两状态操作)
Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly.
共享系统资源要求操作系统确保有误程序不会引起其他程序的运行错误Provide hardware support to differentiate between at least two modes of operations.
至少在两个运行状态之间提供硬件支持- User mode – execution done on behalf of a user.
用户态-代表用户执行 - Monitor mode (also supervisor mode or system mode) – execution done on behalf of operating system.
管态（特权模式或系统模式）-代表操作系统执行
- User mode – execution done on behalf of a user.
mode bit added to computer hardware to indicate the current mode: monitor (0) or user (1)
模式位添加到计算机硬件，表示当前模式- mode bits in PSW
at boot time, the hardware starts in monitor mode 系统引导时，硬件处于管态
starts user processes in user mode 在用户模式下执行用户进程
when an interrupt or fault occurs hardware switches to monitor mode 出现中断或陷阱，硬件切换到管态
dual-mode protect OS from errant users, and errant users from one another 双模式保护操作系统免受错误用户和错误用户之间的伤害
privileged instructions 特权指令: change mode, I/O 特权指令必须在管态下执行,
- in user mode: always change mode to kernel
- the way to implement system call
- arguments passed via registers, stack, or memory (with pointers in registers or stack)
- in kernel mode: just do it!
- in user mode: always change mode to kernel
I/O Protection
- all I/O instructions are privileged instructions 所有的I/O指令都是特权指令
- memory mapped I/O, disk I/O (file access), display I/O, printer I/O, network I/O
- a user cannot issue I/O instructions directly, he must do it through system call用户不能直接用i/o指令，必须通过系统调用
- it must be ensured that a user program could never gain control of the computer in monitor mode 确保用户程序不能在管态下控制计算机
- e.g., a user program that, as part of its execution, stores a new address in the interrupt vector
- a way to inject a virus or Trojan horse on DOS system
- e.g., a user program that, as part of its execution, stores a new address in the interrupt vector
Use of a system call to perform I/O
当处在用户态的时候发出system call后,会陷入OS总,同时切换到管态,执行相应的I/O操作,完成后切换回用户态
Memory Protection
- must provide memory protection
- at least for the interrupt vector and the interrupt service routines 必须保护中断向量和中断服务程序
- in order to have memory protection, add two registers that determine the range of **legal addresses a program may access ** 确定进程能访问的合法空间
- base register 基址寄存器– holds the smallest legal physical memory address.
- limit register界限寄存器 – contains the size of the range
- memory outside the defined range is protected
在对内存访问时,需要检查寻址地址是否合法,首先检查该地址是否大于基址地址,如果大于则检查是否在界限寄存器中间,如果不在则陷入OS中,正常则继续运行
- every address generated in every instruction in user mode is hardware checked用户态下所生成的每个地址都要经过硬件检查
- base and limit registers can be loaded by only the OS by using a special privileged instruction 只有在OS下通过特权指令才可以更改基址寄存器和界限寄存器
- when executing in monitor mode, the operating system has unrestricted access to both monitor and user’s memory 当在监视器模式下执行时，操作系统可以无限制地访问监视器和用户的内存
- change the (base and limit) registers
- load users’ programs into users’ memory
- dump memory map of those programs in case of errors
- access and modify parameters of system calls
CPU protection
- we must prevent a program from getting stuck in an infinite loop(死循环), or not calling OS services and never returning control to the OS 需防止用户程序陷入死循环或者不调用系统服务且不将控制权返回到OS
- timer 定时器 – interrupts computer after specified period to ensure operating system maintains control
- fixed timer, e.g. 1/32 second
- variable timer, a fixed-rate clock and a counter
- the counter is decremented every clock tick
- when the counter reaches the value 0, an interrupt occurs
The timer(定时器)
- load-timer is a privileged instruction
- before turning over control to the user’s program, the OS ensures that the timer is set to interrupt 设定计时器以便产生中断
- if the timer interrupts, control transfers to the OS, and the user program may be killed or given more time to run定时器中断，控制权会返回给OS
- timer commonly used to implement time sharing 用来实现分时系统
- time slice (every N milliseconds)
- timer also used to compute the current time计算当前时间
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