Computer Systems Architecture CMT603 Operating Systems

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Computer Systems ArchitectureCMT603Operating
Systems

• Ian Cooper
• i.m.cooper_at_cs.cf.ac.uk

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Plan for This session

• Introduce myself
• Talk about the style of the lectures
• Brief introduction to Operating Systems
• Cover a few basic concepts.

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Ian Cooper

• BEng
• Electronics

• Nortel
• Holliday group / iTouch
• Allied Telesyn Research

• MSc Computing
• Writing up PhD

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The Course Info

• INTERACTIVE!!!!!
• 11 hours 1 revision lecture
• Example Exercises
• Reading
• Modern Operating Systems (second edition). Andrew
  S. Tanenbaum. Prentice Hall, 2001.
• Operating System Concepts. Seventh edition.
  Silberschatz Galvin, Addison-Wesley, 2005.
• INTERACTIVE!!!!!

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Examples of Operating Systems.
What is an operating system?
OSX
Windows Mobile
Linux
Mac OS
Android (open handset alliance)
Unix
Windows 95
Windows XP
MS-DOS
Windows Vista
Acorn MOS
Symbian
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What is an operating system?

• What does it do?
• Process Management
• Memory management
• I/O management
• Support functions
• Networking
• User interface
• Security

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Where does it fit in?
Application
Program
Instruction Level
Operating System
Implementation
Instruction Set Architecture
Micro architecture
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Operating System Goals

• Efficiency
• Throughput
• Functionality
• Robustness
• Extensibility
• Portability
• Security
• Interactivity

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Course Contents.

• Introduction
• Processes and Threads
• Scheduling
• Critical Section Algorithms
• Semaphores
• Memory
• Contiguous memory.. Fixed/Variable partition
• Non Contiguous memory.. Paging/Segmentation
• Virtual memory
• File Systems

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Concepts

• Architectures of Operating Systems
• Monolithic
• Layered
• Kernel
• Microkernel
• Virtual Machines
• Increasing Efficiency
• Multi program
• Multi User

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Monolithic Architecture

• Monolithic Architecturethe early operating
  systems
• Every component is contained in the kernel, can
  directly communicate with other components

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Monolithic Architecture

User Space
Applications

OS Layer
System Calls
Computer Hardware
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Monolithic Architecture

• Pros
• Highly efficient by direct intercommunication
  between components
• Cons
• difficult to develop
• difficult to isolate the source of bugs and other
  errors
• particularly susceptible to damage from malicious
  code

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Layered Architecture

• Layered OS structure
• Group components that perform similar functions
  into layers. Each layer communicates only with
  neighbour layer

User Space

Kernel Space
Layer 3 Layer 2 Layer 1 Layer 0
Computer Hardware
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Layered Architecture

• Pros
• It provides good modularity helps simplify the
  development of an OS
• Cons
• Less efficient
• Complex design each functionality has to be
  divided into parts to fit into different layers.

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Kernel Based Architecture

• It separates the machine-independent parts from
  the machine-dependent parts
• Kernel is machine-dependent. It contains the
  basic component of OS.

User Space
Operating System
OS Kernel
Computer Hardware
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Kernel Based Architecture

• Pros
• Better portabilityKernel encloses all the
  machine-dependent code
• Cons
• Suffers similar problem as in layered OSs

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Microkernel Based Architecture

• As OS expanded, the kernel became large and
  difficult to manage
• Microkernel approach removes all nonessential
  components from the kernel and implementing them
  as system and user-level programs.
• Result A smaller kernel

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Microkernel Based Architecture

User Space
Operating System
Microkernel
Computer Hardware
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Microkernel Based Architecture

• Pros
• Enhance portability, extensibility, reliability
  and security
• Cons
• Less efficientincreased system function overhead

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Virtual Machines

• Can create the illusion that there are more than
  one separate machines.

User Space
User Space
User Space
Kernel
Kernel
VM1
VM1
Virtual machine implementation
Host Operating System
Computer Hardware
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Increasing Efficiency

• Multiprogramming
• Try to Keep the CPU busy
• CPU operations take less time than I/O
• When a process waits for I/O operation, OS swaps
  to another process.

Operating System
Job 1
Job 2
Job 3
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Multi User

• Logical extension of Multiprogramming

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Summary

• What an Operating System does
• Where an Operating System fits in
• How an Operating System works
• Architectures of Operating Systems
• Multi user, program

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Question(to think about, you dont have to go
and research this. (yet))

• If the OS is a multiprogramming OS, and the OS
  chooses a job for execution, this job will be
  active in the CPU. This means that (in a single
  processor computer) the OS is not running.
• How does the OS retain control over the computer
  resources in order to swap the jobs???