【操作系统】第一章小结

Chapter 1 Introduction

1）什么是computer system？

答：硬件（CPU、memory、I/O）、操作系统、应用程序、用户。

2）从不同角度理解操作系统

a、user view

用户和硬件之间的接口

b、system view

resource allocator， a control program(especially concerned with I/O)

3）操作系统的定义

4）中断

a、中断对于计算机系统来说非常重要，可以说一个computer system就是由中断来驱动的（interrupt driven）

b、中断可能来自硬件或者软件，硬件通过信号产生中断，软件通过系统调用（system call，也叫monitor call）

5）存储结构

a、主存（RAM）、辅存（一般是磁盘）

b、存储结构：

register、cache、main memory、electronic disk、magnetic disk、optical disk、magnetic tape

在electronic disk之前的都是易失的（volatile），electronic disk有易失的也有非易失的。

6）I/O结构

7）计算机系统的分类

a、单处理器系统（single-processor systems）

如PDA、mainframe

b、多处理器系统（multiprocessor systems）

优点：increased throughput（注意N个处理器提高的比例不是N，要小于N，因为有一部分额外开销），economy of scale（直译为“区域经济”，就是说这个东西规模大了效率高了之类的=。=），increased reliability。多处理器系统分两类：asymmetric和symmetric（简称SMP），前者存在主从关系（master-slave relationship），有一个master processor给其他slave分配任务，后者没有主从关系，处理器是并行的。SMP的典型例子是solaris。

c、集群系统（clustered system）

和多处理器系统很相似。意思是共享存储器，通过LAN或者其他什么手段互联起来的一堆计算机。

8）操作系统的结构

a、多道程序（multiprogramming）

意思就是程序被放进内存里，CPU可以灵活地在它们之间分配时间，比如做任务1的时候，做着做着发现任务1要I/O10分钟，那CPU就先不管它，跳去做任务2，当然最后还是要回来处理任务1的。由此引出的一个概念是time-sharing（multitasking）。

9）operating system operations

区分用户态（user mode）、内核态（kernel mode）、特权指令（privileged instructions）和非特权指令（unprivileged instructions）。一般来说下面的指令是特权指令：I/O相关，timer相关，从内核态切换到用户态（反过来不是），中断相关，清理内存等。

10）进程管理、内存管理、存储器管理等

略

11）保护和安全

略

12）分布式系统

略

13）特殊用途的系统

a、实时嵌入式系统

b、多媒体系统

c、手持系统

14）计算环境

a、traditional computing

b、client-server computing

c、peer-to-peer computing

d、web-based computing

附一个课后题的答案：

Answer:

a. Batch. Jobs with similar needsare batched together and run through the computer as a group by an operator orautomatic job sequencer. Performance is increased by attempting to keep CPU andI/O devices busy at all times through buffering, off-line operation, spooling,andmultiprogramming. Batch is good for executing large jobs that need littleinteraction; it can be submitted and picked up later.

b. Interactive. This system iscomposed of many short transactions where the results of the next transactionmay be unpredictable. Response time needs to be short (seconds) since the usersubmits and waits for the result.

c. Time sharing. This systems usesCPU scheduling and multiprogramming to provide economical interactive use of asystem. The CPU switches rapidly from one user to another. Instead of having ajob defined by spooled card images, each program reads its next control cardfrom the terminal, and output is normally printed immediately to the screen.

d. Real time. Often used in adedicated application, this system reads information from sensors and mustrespond within a fixed amount of time to ensure correct performance.

e. Network. Provides operatingsystem features across a network such as file sharing.

f. SMP. Used in systems where thereare multiple CPU’s each running the same copy of the operatingsystem.Communication takes place across the system bus.

g. Distributed.This systemdistributes computation among several physical processors. The processors donot share memory or a clock. Instead, each processor has its own local memory.They communicate with each other through various communication lines, such as ahigh-speed bus or local area network.

h. Clustered. A clustered systemcombines multiple computers into a single system to perform computational taskdistributed across the cluster.

i. Handheld. A small computer systemthat performs simple tasks such as calendars, email, and web browsing. Handheldsystems differ from traditional desktop systemswith smallermemory and displayscreens and slower processors.