操作系统的演变及模型

1 .Advanced Operating Systems (CS 202) OS Evolution and Organization Jan, 13, 2016 

2 . Expectations and little bit about me •  I am NOT an OS person –  I drew the short straw J •  My second time teaching this class –  My favorite two answers are •  I don’t know •  What do YOU think? –  I am looking forward to learn with you •  …but I do know a lot about OS –  I am a systems person –  I work in architecture, networking, high performance computing and security •  OS is at the intersection of all systems areas 2 

3 . Coming up •  Reading for next week (Extensibility): –  For Wednesday, Spin (critique) and Exokernel –  Friday, L4 –  Links on class website •  Programming assignment released Monday –  Optional Lab0 released today 3 

4 . Today •  Evolution of Operating Systems (and computers!) –  Some slides modified from Silberschatz and Gavin, as well as Margo Seltzer •  Operating Systems models •  Why study history? –  Understand why OS’s look like they are –  Appreciate how and why different pieces evolved –  Explain how external forces also shape OS –  Provide context for the rest of the quarter –  Its interesting! 4 

5 . Dawn of computing program CPU printer •  Pre 1950 : the very first electronic computers –  valves and relays –  single program with dedicated function •  Pre 1960 : stored program valve machines –  single job at a time; OS is a program loader 5 

6 . Phase 0 of OS Evolution (40s to 1955) •  No OS –  Computers are exotic, expensive, large, slow experimental equipment –  Program in machine language and using plugboards –  User sits at console: no overlap between computation, I/O, user thinking, etc.. •  Program manually by plugging wires in •  Goal: number crunching for missile computations •  Imagine programming that way –  Painful and slow 6 

7 . OS progress in this period •  Libraries of routines that are common –  Including those to talk to I/O devices –  Punch cards (enabling copying/exchange of these libraries) a big advance! –  Pre-cursor to OS 7 

8 . Phase 1: 1955-1970 •  Computers expensive; people cheap –  Use computers efficiently – move people away from machine –  OS becomes a batch monitor •  Loads a job, runs it, then moves on to next •  If a program fails, OS records memory contents somewhere •  More efficient use of hardware but increasingly difficult to debug 8 

9 .•  Batch systems on mainframe computers –  collections of jobs made up into a batch –  example: IBM 1401/7094 •  card decks spooled onto magnetic tape and from tape to printer –  example: English Electric Leo KDF9 •  32K 48-bit words, 2µsec cycle time •  punched paper-tape input ‘walk-up’ service or spooling via mag tape 9 

10 .Advances in technology in this stage •  Data channels and interrupts –  Allow overlap of I/O and computing –  Buffering and interrupt handling done by OS –  Spool (buffer) jobs onto “high speed” drums 10 

11 . Phase 1, problems •  Utilization is low (one job at a time) •  No protection between jobs •  Short jobs wait behind long jobs –  So, we can only run one job at a time •  Coordinating concurrent activities •  Still painful and slow (but less so?) 11 

12 .Advances in OS in this period •  Hardware provided memory support (protection and relocation) •  Multiprogramming (not to be confused with time sharing) •  Scheduling: let short jobs run first •  OS must manage interactions between concurrent things –  Starts emerging as a field/science •  OS/360 from IBM first OS designed to run on a family of machines from small to large 12 

13 . Some important projects •  Atlas computer/OS from Manchester U. (late 50s/early 60s) –  First recognizable OS –  Separate address space for kernel –  Early virtual memory •  THE Multiprogramming system (early 60s) –  Introduced semaphores –  Attempt at proving systems correct; interesting software engineering insights 13 

14 . Not all is smooth •  Operating systems didn’t really work •  No software development or structuring tools; written in assembly •  OS/360 introduced in 1963 but did not really work until 1968 –  Reported on in mythical man month •  Extremely complicated systems –  5-7 years development time typical –  Written in assembly, with no structured programming –  Birth of software engineering? 14 

15 . Phase 2: 1970s •  Computers and people are expensive –  Help people be more productive –  Interactive time sharing: let many people use the same machine at the same time –  Emergence of minicomputers •  Terminals are cheap –  Keep data online on fancy file systems –  Attempt to provide reasonable response times (Avoid thrashing) 15 

16 . Important advances and systems •  Compatible Time-Sharing System (CTSS) –  MIT project (demonstrated in 1961) –  One of the first time sharing systems –  Corbato won Turing award in 1990 –  Pioneered much of the work in scheduling –  Motivated MULTICS 16 

17 . MULTICS •  Jointly developed by MIT, Bell Labs and GE •  Envisioned one main computer to support everyone –  People use computing like a utility like electricity – sound familiar? Ideas get recycled •  Many many fundamental ideas: protection rings, hierarchical file systems, devices as files, … •  Building it was more difficult than expected •  Technology caught up 17 

18 . Sabre system •  System to run airline systems –  Still in use! •  Minicomputer (then) with terminals for reservation agents •  Important ideas such as transaction processing 18 

19 . Unix appears •  Ken Thompson, who worked on MULTICS, wanted to use an old PDP-7 laying around in Bell labs •  He and Dennis Richie built a system designed by programmers for programmers •  Originally in assembly. Rewritten in C –  If you notice for the paper, they are defending this decision –  However, this is a new and important advance: portable operating systems! •  Shared code with everyone (particularly universities) 19 

20 . Unix (cont’d) •  Berkeley added support for virtual memory for the VAX •  DARPA selected Unix as its networking platform in arpanet •  Unix became commercial –  …whicheventually lead Linus Torvald to develop Linux 20 

21 .Some important ideas in Unix •  OS written in a high level language •  OS portable across hardware platforms –  Computing is no longer a pipe stove/vertical system •  Pipes •  Mountable file systems •  Many more (we’ll talk about unix later) 21 

22 . Phase 3: 1980s •  Computers are cheap, people expensive –  Put a computer in each terminal –  CP/M from DEC first personal computer OS (for 8080/85) processors –  IBM needed software for their PCs, but CP/M was behind schedule –  Approached Bill Gates to see if he can build one –  Gates approached Seattle computer products, bought 86- DOS and created MS-DOS –  Goal: finish quickly and run existing CP/M software –  OS becomes subroutine library and command executive 22 

23 . New technologies in Phase 3 •  Personal workstations –  The PERQ –  Xerox Alto –  SUN workstation •  Personal computers –  Apple II –  IBM PC –  Macintosh 23 

24 . New technologies (cont’d) •  Business applications! –  Word processors –  Spreadsheets –  Databases •  Marketplace is broken up horizontally –  Hardware –  OS –  Applications 24 

25 . New advances in OS •  PC OS was a regression for OS –  Stepped back to primitive phase 1 style OS leaving the cool developments that occurred in phase 2 •  Academia was still active, and some developments still occurred in mainframe and workstation space 25 

26 . Phase 4: Networked systems 1990s to 2010s •  Machines can talk to each other –  its all about connectivity •  We want to share data not hardware •  Networked applications drive everything –  Web, email, messaging, social networks, … •  Protection and multiprogramming less important for personal machines –  But more important for servers 26 

27 . Phase 4, continued •  Market place continued horizontal stratification –  ISPs (service between OS and applications) –  Information is a commodity –  Advertising a new marketplace •  New network based architectures –  Client server –  Clusters –  Grids –  Distributed operating systems –  Cloud computing (or is that phase 5?) 27 

28 . New problems •  Large scale –  Google file system, mapreduce, … •  Concurrency at large scale –  ACID(Atomicity, Consistency, Isolation and Durability) in Internet Scale systems •  Very large delays •  Partitioning •  Security and Privacy 28 

29 . Phase 5 2010s -- ?? •  New generation? •  Mobile devices that are powerful •  Sensing: location, motion, … •  Cyberphysical systems •  Computing evolving beyond networked systems –  But OS for them looks largely the same –  Is that a good idea? 29