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Advanced Operating Systems

20MCA

(Elective )

Contents

• (^) Overview : Functions of Operating System– Design Approaches – Types of Advanced Operating Systems.
• (^) Synchronization Mechanisms : Concept of Processes and Threads –The Critical Section Problem – Other Synchronization Problems:– Monitor –Serializer – Path Expressions.
• (^) Distributed Operating Systems :- Issues in Distributed Operating System – Communication Networks And Primitives Lamport’s Logical clocks – Causal Ordering of Messages. (Mukesh Singhal and Niranjan G. Shivaratri, “ Advanced Concepts in Operating Systems - Distributed, Database, and Multiprocessor Operating Systems”, Tata McGraw-Hill, 2001.)

What is Advanced OS?

• (^) Traditional Operating System : which ran on stand- alone computers with

single processors.

• (^) Arise of Multiprocessor Systems and Distributed Systems.
• (^) Due to the high demand and popularity of multiprocessor systems,

advanced operating system have gained high importance.

Functions of an Operating System

Two basic functions of operating systems are:

1. Resource management

2. User friendliness

Functions of an Operating System...

2. User friendliness

• (^) It hides the unpleasant, low-level details and singularity of bare H/W machine.
• (^) Friendlier interface to the machine.
• (^) It encompasses the following functions.
  • (^) Execution environment (Process management – creation, control, and termination, file manipulation, interrupt handling, support for I/O operations. Language support).
  • (^) Error detection and handling
  • (^) Protection and security
  • (^) Fault tolerance and failure recovery.

Design Approaches

• A typical operating system that supports a multiprogramming environment can easily be tens of megabytes in length and its design, implementation, and testing amounts to the undertaking of a huge software project.
• Deal with complexities of modern systems.
• How and what should be done in the context of operating systems
• Separation of Policies and Mechanisms
  • (^) Policies - What should be done
  • (^) Mechanisms - How it should be done
  • (^) Ex: In CPU scheduling, mechanisms provide the means to implement various scheduling disciplines and policy decides which CPU scheduling discipline will be used.

Layered Approach

• This approach divides the operating system into several layers.
• (^) Each layer has well-defined functionality and input-output interfaces with the two adjacent layers.
• The bottom layer interfaces with machine hardware and top layer interfaces with users or operators.
• (^) This approach has all the advantages of modular design.
• Each layer can be designed, coded and tested independently.
• (^) This approach simplifies the design, specification, and implementation of an operating system.
• Drawback : functions must be carefully assigned to various layers because a layer can make use only of the functionality provided by the layers beneath it.
• Example : THE operating system and MULTICS operating system

Layered Approach

• (^) Example is THE Operating System which consists of six layers.

Kernel Approach

• (^) An operating system is an orderly growth of software over the kernel where all decisions regarding process scheduling, resource allocation, execution environment, file system, and resource protection, etc. are made.
• (^) A kernel should contain a minimal set of functionality that is adequate to build an operating system with a given set of objectives.
• (^) Including too much functionality in a kernel results in low flexibility at a higher level, whereas including too little functionality in a kernel results in low functional support at a higher level.
• (^) Example : C.mmp (Kernal is Hydra)

Kernel Approach

Virtual Machine Approach

• (^) Illusion of multiple instances of hardware

Types of Advanced Operating Systems

• (^) The impetus for advanced operating systems has from 2 dimensions.
  1. it has come from advanced operating systems of multicomputer systems and is driven by a wide variety of high-speed architectures
  2. advanced operating systems driven by applications Types
  3. Distributed operating systems
  4. Multiprocessor operating systems
  5. Database operating systems
  6. Real-time operating systems

1. Distributed operating systems

• (^) Are operating systems for a network of autonomous computers connected by a communication network.
• (^) Controls and manages the hardware and software resources of a distributed system such that its users view the entire system as a powerful monolithic computer system.
• When a program is executed in a distributed system, the user is not aware of where the program is executed or of the location of the resources accessed.
• (^) Practical issues:
  • lack of shared memory
  • lack of global clock
  • unpredictable communication delays.

2. Multiprocessor operating systems

• (^) Consists of a set of processors that shares a set of physical memory blocks over interconnection network.
• (^) Is a tightly coupled system where the processors share an address space.
• (^) Controls and manages the hardware and software resources such that users view the system as a powerful uniprocessor system
• (^) User is not aware of the presence of multiple processors and the interconnection network
• (^) Practical issues:
  • increased complexity of synchronization, scheduling, memory management, protection and security.