Operating System Overview - Operating Systems - Lecture Slides, Slides of Computer Science

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Operating Systems

Lecture 04:

Operating System Overview

Today

• Announcements:
• Operating Systems Overview:
  • Main concepts in OS
  • OS structure
  • Virtual Machines
  • Windows vs. Unix vs. Linux: study cases

Process

• Fundamental to the structure of operating systems
• Many definitions have been given , including
  • A program in execution
  • An instance of a program running on a computer
  • The entity that can be assigned to and executed

on a processor

• A unit of activity characterized by a single

sequential thread of execution, a current state,

and an associated set of system resources

Development of the Process

 Three major lines of computer system development created

problems in timing and synchronization that contributed to the

development of the process concept:

• processor is switched among the various programs residing in main memory

multiprogramming batch operation

• be responsive to the individual user but be able to support many users simultaneously

time sharing

• a number of users are entering queries or updates against a database

real-time transaction systems

Components of

a Process

• The execution context is essential: - it is the internal data by which the OS is able to supervise and control the process - includes the contents of the various process registers - includes information such as the priority of the process and whether the process is waiting for the completion of a particular I/O event
• A process contains

three components:

• an executable program
• the associated data needed by the program (variables, work space, buffers, etc.)
• the execution context (or “process state”) of the program

Process Management

 The entire state of the

process at any instant is

contained in its context

 New features can be

designed and incorporated

into the OS by expanding

the context to include any

new information needed to

support the feature

Virtual Memory

• A facility that allows programs to address

memory from a logical point of view, without

regard to the amount of main memory physically

available

• Conceived to meet the requirement of having

multiple user jobs reside in main memory

concurrently

Paging

• Allows processes to be comprised of a number of fixed-

size blocks, called pages

• Program references a word by means of a virtual address
  • consists of a page number and an offset within the page
  • each page may be located anywhere in main memory
• Provides for a dynamic mapping between the virtual

address used in the program and a real (or physical)

address in main memory

Virtual Memory

Addressing

Key Elements for

Resource Scheduling

Microkernel Architecture

• Assigns only a few essential functions to the

kernel:

– The approach:

address spaces

interprocess communication (IPC)

basic scheduling

simplifies implementation

provides flexibility

is well suited to a distributed environment

Multithreading

• Technique in which a process, executing an application, is

divided into threads that can run concurrently

Thread

• dispatchable unit of work
• includes a processor context and its own data area to enable subroutine branching
• executes sequentially and is interruptible Process
• a collection of one or more threads and associated system resources
• programmer has greater control over the modularity of the application and the timing of application related events

SMP Advantages

Performance

more than one process can be running simultaneously, each on a different processor

Availability failure of a single process does nothalt the system

Incremental Growth

performance of a system can be enhanced by adding an additional processor

Scaling

vendors can offer a range of products based on the number of processors configured in the system

Multiprogramming vs.

Multiprocessing