第二章 HYZ-OS-2017-1-操作系统引论-1.ppt

* Same as IP layer…. * * * * * * * * OS first appeared as a subroutine “library” shared by all users. Library: pull card decks from wall. * Multiprogramming: 2 jobs (1 takes 10 hrs, the other 10 mins). Don’t have to wait 10 hrs! lists 1777 people who “contributed to Multics”. Probably 30-40 core developers. * Compare to 500Gb 2.5” disks, 80 Gbyte 1.8” disks * Computers are friendly things: 1 terminal, feed me. Add another terminal, feed me. Can you keep doing this? NO! Eventually fall off a cliff (add one more user, computer slows down by a factor of 1000) * No, Feature creep. PC made OS a subroutine all over again. But then realized even single users need memory protection, multiprogramming, etc. Same is true of PDAs and phones * Why do we need distributed systems? Resource sharing (printers, Internet connections,…) and info sharing (files, email, IM, …) * * * * * How many people have written a 1K program? 15 pages How many people have written a 10K program? 150 pages * 北京交通大学计算机学院何永忠 * 多道批处理系统优点 优点 系统资源利用率高 系统吞吐量大 * 北京交通大学计算机学院何永忠 * Fran Allenthe first female to win Turing Award Who took a temporary job as a programmer at IBM to pay for her student loans, but she stayed at IBM for 45 years, and is the first female to win Turing Award for her work in high performance computing in 2006 * 北京交通大学计算机学院何永忠 * Fran Allen Allen当时在IBM650上编程。她需要了解机器结构，并使用汇编语言。一次深夜，操作员打电话给她，因为她计划在晚上运行的程序出错了。Allen放下电话思考，突然她意识到数据校验算法没有处理一种特殊的情况，马上打电话回去告诉了操作员修改。 还有一天早上，一个喜欢晚上工作的雇员—这是个令人生畏的人，体型庞大又非常严肃—把一大叠调试列表扔到Allen面前，指着其中一bit说：“为什么把这一bit置位？”，他为一个问题想了一整夜。 -- Coder at Work * 北京交通大学计算机学院何永忠 * History Phase 2 (1970 – 1985)Hardware Cheaper, Humans Expensive 主机造价降低到几千美元 批处理的问题 交互性差，对用户不友好 具体表现：难于调试、不能支持编辑、不能玩游戏 交互式分时系统: 一台主机、多个廉价的终端(~$1000) 、多用户同时以交互方式使用计算机（不同于C/S模式） 便于用户程序编辑修改、调试、直接控制 Sacrifice CPU time to get better response time * 北京交通大学计算机学院何永忠 * 分时系统 * 北京交通大学计算机学院何永忠 * 分时系统实现 及时处理 作业应直接进入内存 与批处理系统用户作业先进入磁盘再调入内存不同 在不长的时间内就能使每个作业都运行一次 时分复用：时间片轮转策略，把CPU时间划分成很多段，每一段