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Dr. Christian Vecchiola Postdoctoral Research Fellow Cloud Computing and Distributed Systems (CLOUDS) Lab Dept. of Computer Science.

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Presentation on theme: "Dr. Christian Vecchiola Postdoctoral Research Fellow Cloud Computing and Distributed Systems (CLOUDS) Lab Dept. of Computer Science."— Presentation transcript:

1 Dr. Christian Vecchiola Postdoctoral Research Fellow Cloud Computing and Distributed Systems (CLOUDS) Lab Dept. of Computer Science and Software Engineering The University of Melbourne Operating System Architecture and Distributed Systems Most concepts are drawn from Chapter 6 © Pearson Education

2 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Outline  Introduction  OS / Kernel Models – Monolithic Operating Systems – Layered Systems – Traditional Operating Systems – Micro-kernel Operating Systems  Micro-kernel Operating Systems – Observations – Architecture – Client Server Model – Comparison  Hybrid Approaches  Summary

3 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  Why Operating Systems? – OSes are a fundamental component of today’s computing systems. – They offer a set of services for: Managing the hardware resources of devices Scheduling the execution of the applications Simplifying the development of applications – OSes constitute a common sub-stratus for (almost) all the applications …. …. even distributed system middleware

4 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  A little bit of history… – Pre-OS software development (before 60s) Single task model (one application running) Developers had to: – Program the system from booting the hardware up.. – Manage every aspect of the system Assembly language Very challenging Model: Machine + Program + Data = Application

5 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  A little bit of history… – The OS era (60s onwards) Evolution from single task to multi-tasking There exist a common program that –.. is loaded before any other program –.. manages the hardware resources of the machine –.. schedules the execution of user applications (one or more) –.. provides a higher level interface to the system Development of compilers Model: Application + OS +Machine = Execution

6 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  What does an OS do? – Manages the hardware resources Memory CPU Disks – Provides access to connected devices (drivers) Printers Cameras Scanners… – Manages and Schedules applications Simple user applications Services

7 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  Ehy… are we studying DS…? – OSes are a fundamental component in DS – They provide the basic services for what concerns Network connectivity Machine resources management Concurrency and IPC Access to the file system – Distributed Systems are based on middleware it is “just another” application for the OS it might be a fundamental part of the OS

8 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  DS-wanted features of an OS – Let us look into the architecture of a kernel suitable for a distributed system. – A key principle of DS is openness and with this in mind let us examine the major kernel architectures: Monolithic kernels Layered architecture-based kernels Micro-kernels

9 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  DS-wanted features of an OS – An open DS should make it possible to: Run only that system software on each computer that is necessary for its particular role in the system architecture: – Avoiding redundant modules on capability-limited devices. – Optimizing the behavior of specific components in different scenarios (server, client, ….) Allow the software (and the computer) implementing any particular service to be changed independent of other facilities. Allow for alternatives of the same services to be provided, when this is required to suit different users or applications. Introduce new services without harming the integrity of existing ones. – Which features are required by an OS to expose these properties?

10 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Introduction  A Guiding principle of OS design – For example, an ideal scheduling system would provide mechanisms that enable a multimedia application such as videoconferencing to meet its real-time demands while coexisting with a non-real-time application such as web browsing. – That is kernel would provide only the most basic mechanisms upon which the general resource management tasks at a node are carried out. – Server modules would be dynamically loaded as required, to implement the required RM policies for the currently running applications. Separation of fixed resource management “mechanisms“ from resource management “policies”, which vary from application to application and service to service.

11 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms OS / Kernel Models  Main Design Principles – The two key examples of kernel design approaches are: Monolithic Microkernel – Key difference: what does belong to the kernel? – Three main models: Monolithic OS Layered OS Microkernel-based OS – The first two can be considered monolithic. The chambers 20th century dictionary definition of monolithic is: a pillar, column, of a single stone: anything that resembling a monolithic, massiveness.

12 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms  Monolithic Kernel vs Micro-Kernel OS / Kernel Models Monolithic KernelMicro-Kernel Server: Dynamically loaded server program: Kernel code and data: S2S3S4 S1 S2 S3S4 S1

13 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms OS / Kernel Models  Operating System Models – Serve as frameworks that unify capabilities, services and tasks to be performed – Three approaches to building OS.... Monolithic OS Layered OS Microkernel based OS – Client server OS – Suitable for distributed systems – Simplicity, flexibility and high performance are crucial for OS.

14 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms OS / Kernel Models  Monolithic Kernels – Better application performance – Hard to extend – Example: MS-DOS Application Programs Application Programs System Services Hardware User Mode Kernel Mode Application Programs Application Programs

15 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms OS / Kernel Models  Layered Operating Systems User Mode Kernel Mode Memory & I/O Device Mgmt Process Scheduler Application Programs Application Programs Application Programs Application Programs System Services Hardware

16 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms  Traditional Operating Systems OS / Kernel Models OS Designer OS User Mode Kernel Mode Application Programs Application Programs Application Programs Application Programs

17 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Observations – Monolithic Operating Systems are: Massive: they perform all basic OS functions and take up in the order of megabytes of code and data. Undifferentiated: they are coded in a non-modular way (traditionally) although modern ones are much more layered. Intractable: altering any individual software component to adapt it to changing requirements is difficult.

18 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Observations – New trend in Operating System Design User Mode Kernel Mode Hardware Microkernel (very basic functions) Servers Application Programs Application Programs Application Programs Application Programs

19 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Micro-Kernel Operating Systems – Compared to monolithic, microkernel design provides only the most basic abstractions, principally address space, threads and local IPC. – All other system services are provided by servers that are dynamically loaded precisely those computers in the DS that require them. – Clients access these system services using the kernel’s message based invocation mechanisms.

20 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Client Server Model – Tiny OS kernel providing basic primitive (process, memory, IPC) – Traditional services becomes subsystems – OS = Microkernel + User Subsystems – Examples: Mach, PARAS, and Chorus Client Application Client Application OS Emulators File Server File Server Network Server Network Server Display Server Display Server Microkernel Hardware User Kernel Send Reply

21 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Architecture – Micro-Kernels are a layer between H/W and system systems. If performance is goal, rather than portability, then middleware may use facilities of the kernel directly. – Micro-Kernels support middleware as subsystems.

22 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Examples of Micro-Kernels – MACH, CMU It supports different OS emulators (Unix and OS/2). (Mach only) base for OS X – PARAS, C-DAC – Chorus – QNX, – (Windows NT) combination of layered and microkernel.... but massive code.

23 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Micro-Kernel Operating Systems  Comparison – Micro-Kernel main advantages: Extensibility and its ability to enforce modularity behind memory protection boundaries A relative small kernel is more likely to free of bugs than one that is larger and complex. – Monolithic OS main advantage: Relative efficiency with which operations can be invoked is high because even invocation to a separate user-level address space on the same node is more costly.

24 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Hybrid Approaches  Which is the trend today? – Many modern OS follow hybrid approach in OS structure. E.g., Windows NT. – Pure microkernel OSs such as Chorus & Mach have changed over a time to allow servers to be loaded dynamically into the kernel address space or into a user-level address space. – Some OSs such as SPIN used event-based model as a mechanism for interaction between modules grafted into the kernel address space.

25 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Summary  What did we learn? – Operating system provides various types of facilities to support middleware for distributed system: encapsulation, protection, concurrent access management of node resources. – New OS designs provide flexibility in terms of separating mechanisms from policies.

26 Operating System Architecture and Distributed Systems Distributed Systems Principles and Paradigms Additional References Tanenbaum, A.S, Modern Operating Systems, 2nd /3rd Editions, Prentice Hall, ISBN / Silbershatz, A., Galvin, P.B., Gagne, Modern Operating Systems, 8 th Editions, Wiley, ISBN


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