CSCI 350 Ch. 1 Introduction to OS Mark Redekopp Ramesh Govindan - - PowerPoint PPT Presentation

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CSCI 350 Ch. 1 Introduction to OS Mark Redekopp Ramesh Govindan - - PowerPoint PPT Presentation

Mar 11, 2024 340 likes •503 views

1 CSCI 350 Ch. 1 Introduction to OS Mark Redekopp Ramesh Govindan and Michael Shindler 2 Syllabus Website (http://bits.usc.edu/cs350) People Projects PintOS Policies Grading & Exams 3 WHAT IS AN OPERATING

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CSCI 350

  • Ch. 1 – Introduction to OS

Mark Redekopp Ramesh Govindan and Michael Shindler

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Syllabus

  • Website (http://bits.usc.edu/cs350)
  • People
  • Projects

– PintOS – Policies

  • Grading & Exams
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WHAT IS AN OPERATING SYSTEM

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Definition

  • A piece of software that

manages a computer’s resources

  • What resources need

managing?

– CPU (threads and processes) – Memory (Virtual memory, protection) – I/O (Abstraction, interrupts, protection)

DISK Processor Mem. Management Unit Network Graphics I/O Drivers & Protocols File Systems Memory Translation Processes & Scheduling System Library System Library User App User App

Kernel Mode Hardware User mode

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HISTORY OF OPERATING SYSTEMS

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Evolution

  • Single job systems

– https://www.youtube.com/watch?v=XetHU_pAWOo

  • Batch systems: OS little more than a library for I/O

– Execute the next program while outputting results from the previous – Better than before since computer wasn’t idle when processing

  • Multi-tasking: DMA, direct I/O access, virtual machines

– Avoided I/O waiting, multiplex CPU and I/O – Virtual machines were developed around this time

  • Time sharing: Support interactive use of computers

– Isolation (privileges), the process abstraction, memory hardware, virtual memory

  • PCs: bitmapped displays, window management
  • Mobile: SSDs, sensors/GPS, touch screen
  • Servers: Virtualization, optimize for specific tasks

As a result of Moore's Law, features available on higher end devices find their way into lower end devices over time. Supercomputer -> server -> desktop -> mobile

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Kinds of Operating Systems

  • General Purpose

– Laptop, Desktop

  • Server

– User and other access policies – Supporting virtualization (hypervisor)

  • Mobile
  • Embedded

– Hard and Soft Real-time

  • Hard Real-time: Missing a deadline results in failure
  • Soft Real-time: Performance/usefulness degrades if deadlines

missed

  • Scheduling, priority, and deterministic latency
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Genealogy of Operating Systems

Figure 1.9, OS:PP 2nd Ed.

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Roles

  • Textbook regularly revisits 3 roles an OS plays:
  • Referee

– Protection against other applications – Enforce fair resource sharing

  • Why doesn't an infinite loop require a reboot?
  • Illusionist (Virtualization)

– Each program thinks it is running separately – Each program thinks it has full access to computer's resources (or unlimited resources)

  • Glue

– Common services (such as copy/paste) – Files can be read by any application – UI routines for look & feel – Separate applications from hardware

  • so you don’t need to know which keyboard, disk drive, etc
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Case Study of Roles

  • What roles {Referee, Illusionist, Glue} would

be relevant and important in the following systems?

  • Web browser
  • Cloud computing
  • Multiuser database
  • The Internet
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Case Study of Roles

  • Web browser

– Referee (execution of scripted code), glue (display and network functionality) – Illusionist (handling of network errors)

  • Cloud computing

– Illusionist (no need to know where data is stored) and glue (to provide APIs and access) to data – Referee and Illusionist (virtualization, separation)

  • Multiuser Database

– Illusionist (replication and transactions) – Referee (access rights)

  • Internet

– Illusionist (DNS translation, IP routing, Reliability) – Referee (Quality-of-Service, congestion, denial of service) – Glue (Common API, standards, etc.)

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OS Design Criteria (Metrics)

  • Reliability (availability)
  • Security/Privacy
  • Performance
  • Portability & Adoption
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Reliability vs. Availability

  • Reliable: Outputs are as intended for the given

set of inputs

– If outputs are not as intended we say the system has failed

  • Availability: System can do work
  • Available does not imply reliable

– System can be available but not reliable (bugs!) – System can be reliable yet not available

  • DoS, Crash after every instruction but saves results
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Security

  • Security means avoiding compromised states

– Example: Execution of malware/virus

  • Privacy implies only authorized users can

access certain data

  • Security is hard to achieve without sacrificing
  • ther important aspects like performance (e.g.

encryption, translation, etc.)

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Performance

  • Scheduling and Fairness

– Predictability

  • Throughput vs. response time
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Portability

  • OS can abstract applications from various hardware changes

– OS should play middle man and provide an API or AMI (Abstact Machine Interface)

  • Can OS itself be abstracted from hardware changes (i.e. easily

ported to another HW platform)

– Many OSs use a HAL (hardware abstraction layer) so that the bulk of the code need not change as it is migrated to a new platform

  • Adoption: The more devices that can be supported the

greater the chance of adoption

– Network effect: Adoption based on – If good apps are available, OS will be adopted. But good apps may not be written unless the OS is widely adopted.