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Opera&ng Systems: Principles and Prac&ce Tom Anderson
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Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Jul 22, 2020

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Page 1: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Opera&ng  Systems:    Principles  and  Prac&ce  

Tom  Anderson  

Page 2: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

How  This  Course  Fits  in  the  UW  CSE  Curriculum  

•  CSE  333:  Systems  Programming  – Project  experience  in  C/C++  – How  to  use  the  opera&ng  system  interface  

•  CSE  451:  Opera&ng  Systems  – How  to  make  a  single  computer  work  reliably  – How  an  opera&ng  system  works  internally  

•  CSE  452:  Distributed  Systems  (winter  2015)  – How  to  make  a  set  of  computers  work  reliably,  despite  failures  of  some  nodes  

Page 3: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Project:  OS/161  

•  Build  an  opera&ng  system    –  That  can  boot  on  a  mul&processor  

•  We  give  you  some  basic  building  blocks  –  Three  assignments,  that  build  on  each  other  

•  Threads,  user  programs,  virtual  memory  

– Work  in  groups  of  2-­‐3  (recommend  3!)  

•  Instruc&ons  on  web  page  – Download  and  browse  code  before  sec&on  –  Bring  laptop  or  smartphone  to  sec&on  

•  Assignment  0  due  next  Friday  

Page 4: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Problem  Sets  

•  Three  assignments  spread  over  quarter  – Prac&ce  for  final  – Done  individually  

Page 5: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Main  Points  (for  today)  

•  Opera&ng  system  defini&on  – SoZware  to  manage  a  computer’s  resources  for  its  users  and  applica&ons  

•  OS  challenges  – Reliability,  security,  responsiveness,  portability,  …  

•  OS  history  – How  are  OS  X,  Windows  8,  and  Linux  related?  

Page 6: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

What  is  an  opera&ng  system?  

•  SoZware  to  manage  a  computer’s  resources  for  its  users  and  applica&ons  

TCP/IP Networking

Virtual Memory

Hardware-Specific Software and Device Drivers

File System

Scheduling

Graphics Processor

Address TranslationProcessors

Network

Hardware

Users

User-mode

Kernel-modeKernel-user Interface

(Abstract virtual machine)

Hardware Abstraction Layer

APP

SystemLibrary

APP

SystemLibrary

APP

SystemLibrary

Disk

Page 7: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Opera&ng  System  Roles  

•  Referee:  –  Resource  alloca&on  among  users,  applica&ons  –  Isola&on  of  different  users,  applica&ons  from  each  other  –  Communica&on  between  users,  applica&ons  

•  Illusionist  –  Each  applica&on  appears  to  have  the  en&re  machine  to  itself  

–  Infinite  number  of  processors,  (near)  infinite  amount  of  memory,  reliable  storage,  reliable  network  transport  

•  Glue  –  Libraries,  user  interface  widgets,  …  

Page 8: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Example:  File  Systems  

•  Referee  –  Prevent  users  from  accessing  each  other’s  files  without  permission  

–  Even  aZer  a  file  is  dele&ng  and  its  space  re-­‐used  •  Illusionist  –  Files  can  grow  (nearly)  arbitrarily  large  –  Files  persist  even  when  the  machine  crashes  in  the  middle  of  a  save  

•  Glue  – Named  directories,  prinf,  …  

Page 9: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Ques&on  

•  What  (hardware,  soZware)  do  you  need  to  be  able  to  run  an  untrustworthy  applica&on?  

Page 10: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Ques&on  

•  How  should  an  opera&ng  system  allocate  processing  &me  between  compe&ng  uses?  – Give  the  CPU  to  the  first  to  arrive?  – To  the  one  that  needs  the  least  resources  to  complete?      To  the  one  that  needs  the  most  resources?  

Page 11: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Example:  web  service  

•  How  does  the  server  manage  many  simultaneous  client  requests?  

•  How  do  we  keep  the  client  safe  from  spyware  embedded  in  scripts  on  a  web  site?  

•  How  do  make  updates  to  the  web  site  so  that  clients  always  see  a  consistent  view?  

Client Server index.html

(1) HTTP GET index.html

(4)HTTP web page

(2)Read file: index.html

(3)File data

Page 12: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

OS  Challenges  

•  Reliability  – Does  the  system  do  what  it  was  designed  to  do?  

•  Availability  – What  por&on  of  the  &me  is  the  system  working?  – Mean  Time  To  Failure  (MTTF),  Mean  Time  to  Repair  

•  Security  –  Can  the  system  be  compromised  by  an  ahacker?  

•  Privacy  –   Data  is  accessible  only  to  authorized  users  

Page 13: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

OS  Challenges  

•  Portability  – For  programs:  

•  Applica&on  programming  interface  (API)  

•  Abstract  virtual  machine  (AVM)  

– For  the  opera&ng  system  •  Hardware  abstrac&on  layer  

TCP/IP Networking

Virtual Memory

Hardware-Specific Software and Device Drivers

File System

Scheduling

Graphics Processor

Address TranslationProcessors

Network

Hardware

Users

User-mode

Kernel-modeKernel-user Interface

(Abstract virtual machine)

Hardware Abstraction Layer

APP

SystemLibrary

APP

SystemLibrary

APP

SystemLibrary

Disk

Page 14: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

OS  Challenges  

•  Performance  –  Latency/response  &me  

•  How  long  does  an  opera&on  take  to  complete?  

–  Throughput  •  How  many  opera&ons  can  be  done  per  unit  of  &me?  

– Overhead  •  How  much  extra  work  is  done  by  the  OS?  

–  Fairness  •  How  equal  is  the  performance  received  by  different  users?  

–  Predictability  •  How  consistent  is  the  performance  over  &me?  

Page 15: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

OS  History  

Descendant

Level 4

Level 5

Level 6

Level 3

Level 2

Level 1

Influence

MVS Multics

MS/DOS VM/370VMS UNIX

Windows BSD UNIX Mach

Windows NT VMWare Linux NEXT MacOS

iOSAndroid

Windows 8 MacOS X

Page 16: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Computer  Performance  Over  Time  1.3 Operating Systems: Past, Present, and Future 27

1981 1997 2014 Factor(2014/1981)

Uniprocessor speed (MIPS) 1 200 2500 2.5K

CPUs per computer 1 1 10+ 10+

Processor MIPS/$ $100K $25 $0.20 500K

DRAM Capacity (MiB)/$ 0.002 2 1K 500K

Disk Capacity (GiB)/$ 0.003 7 25K 10M

Home Internet 300 bps 256 Kbps 20 Mbps 100K

Machine room network10 Mbps(shared)

100 Mbps(switched)

10 Gbps(switched) 1000

Ratio of usersto computers

100:1 1:1 1:several 100+

Figure 1.8: Approximate computer server performance over time, reflecting the most widely used servers ofeach era: in 1981, a minicomputer; in 1997, a high-end workstation; in 2014, a rack-mounted multicoreserver. MIPS stands for “millions of instructions per second,” a measure of processor performance. The VAX11/782 was introduced in 1982; it achieved 1 MIP. DRAM prices are from Hennessey and Patterson,“Computer Architecture: A Quantitative Approach.” Disk drive prices are from John McCallum. The Hayessmartmodem, introduced in 1981, ran at 300bps. The 10 Mbps shared Ethernet standard was alsointroduced in 1981. One of the authors built his first operating system in 1982, used a VAX at his first job,and owned a Hayes to work from home.

from expensive to cheap devices occurred with telephones over the pasthundred years. Initially, telephone lines were very expensive, and a singleline was shared among everyone in a neighborhood. Over time, of course,both computers and telephones have become cheap enough to sit idle untilwe need them.

Despite these changes, operating systems still face the same conceptualchallenges as they did fifty years ago. To manage computer resources for ap-plications and users, they must allocate resources among applications, providefault isolation and communication services, abstract hardware limitations, andso forth. Tremendous progress has been made towards improving the reliabil-ity, security, efficiency, and portability of operating systems, but much more isneeded. Although we do not know precisely how computing technology orapplication demand will evolve over the next 10-20 years, it is highly likelythat these fundamental operating system challenges will persist.

Early Operating SystemsComputers wereexpensive; users

would wait.The first operating systems were runtime libraries intended to simplify theprogramming of early computer systems. Rather than the tiny, inexpensiveyet massively complex hardware and software systems of today, the firstcomputers often took up an entire floor of a warehouse, cost millions of

Page 17: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Early  Opera&ng  Systems:  Computers  Very  Expensive  

•  One  applica&on  at  a  &me  – Had  complete  control  of  hardware  

– OS  was  run&me  library  – Users  would  stand  in  line  to  use  the  computer  

•  Batch  systems  – Keep  CPU  busy  by  having  a  queue  of  jobs  – OS  would  load  next  job  while  current  one  runs  – Users  would  submit  jobs,  and  wait,  and  wait,  and    

Page 18: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Time-­‐Sharing  Opera&ng  Systems:  Computers  and  People  Expensive  

•  Mul&ple  users  on  computer  at  same  &me  – Mul&programming:  run  mul&ple  programs  at  same  &me  

–  Interac&ve  performance:  try  to  complete  everyone’s  tasks  quickly  

– As  computers  became  cheaper,  more  important  to  op&mize  for  user  &me,  not  computer  &me  

Page 19: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Today’s  Opera&ng  Systems:  Computers  Cheap  

•  Smartphones  •  Embedded  systems  

•  Laptops  •  Tablets  •  Virtual  machines  

•  Data  center  servers  

Page 20: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Tomorrow’s  Opera&ng  Systems  

•  Giant-­‐scale  data  centers  •  Increasing  numbers  of  processors  per  computer  

•  Increasing  numbers  of  computers  per  user  

•  Very  large  scale  storage  

Page 21: Operang)Systems:)) Principles)and)Prac&ce) · • Applicaon)programming) interface)(API)) • Abstractvirtual)machine) (AVM)) – For)the)operang)system) • Hardware)abstrac&on)

Textbook  

•  Lazowska,  Spring  2012:  “The  text  is  quite  sophis&cated.  You  won't  get  it  all  on  the  first  pass.  The  right  approach  is  to  [read  each  chapter  before  class  and]  re-­‐read  each  chapter  once  we've  covered  the  corresponding  material…  more  of  it  will  make  sense  then.  Don't  save  this  re-­‐reading  un2l  right  before  the  mid-­‐term  or  final  –  keep  up.”  


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