2-systemstructure-110817130451-phpapp02.pdf

8/14/2019 2-systemstructure-110817130451-phpapp02.pdf

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System Structure

Organized By: Vinay Arora

Assistant Professor

CSED, TU


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Disclaimer

This is NOT A COPYRIGHT MATERIAL

Content has been taken mainly from the following books:

Operating Systems Concepts By Silberschatz & Galvin,Operating Systems: Internals and Design Principles By William Stallings

www.os-book.comwww.cs.jhu.edu/~yairamir/cs418/os2/sld001.htm

www.personal.kent.edu/~rmuhamma/OpSystems/os.html

http://msdn.microsoft.com/en-us/library/ms685096(VS.85).aspx

http://www.computer.howsttuffworks.com/operating-system6.htm

http://williamstallings.com/OS/Animations.htmlhttp://msdn.microsoft.com/en-us/library/aa450566.aspx

www.os-book.com

http://www.yolinux.com/TUTORIALS/ForkExecProcesses.html

Etc


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Operating System Services User Interface - Almost all operating systems have a user interface.

Command-Line (CLI), Graphics User Interface (GUI)

Program Execution - The system must be able to load a programinto memory and to run that program, end execution.

I/O Operations - A running program may require I/O, which mayinvolve a file or an I/O device.

File-System Manipulation - Programs need to read and write filesand directories, create and delete them, search them, list fileInformation, permission management.


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Operating System Services


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Communications Processes may exchange information.

Communications may be via shared memory or through messagepassing.

Error Detection OS needs to be constantly aware of possible errors

May occur in the CPU and memory hardware, in I/O devices orin user program

For each type of error, OS should take the appropriate action.

Debugging facilities


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Operating System Interface - CLI

CLI allows direct command entry

Sometimes implemented in kernel, sometimes by systems

program

Sometimes multiple flavors implemented shells

Primarily fetches a command from user and executes it

Sometimes commands built-in, sometimes just names of

programs If the latter, adding new features doesnt require shell

modification


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CLI


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CLI


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Operating System Interface - GUI User-friendly desktop metaphor interface

Usually mouse, keyboard, and monitor

Icons represent files, programs, actions, etc

Various mouse buttons over objects in the interface cause various

actions (provide information, options, execute function, open

directory (known as a folder)

Many systems now include both CLI and GUI interfaces


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GUI


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Layered View


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System Call Programming interface to the services provided by the OS.

Typically written in a high-level language (C or C++)

The invocation of an operating system routine.

Operating systems contain sets of routines for performing various low-

level operations.

For example, all operating systems have a routine for creating adirectory. If you want to execute an operating system routine from a

program, you must make a system call.


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Mostly accessed by programs via a high-level Application Program

Interface (API) rather than direct system call use.

Why use APIs rather than system calls? There are specific reasons for

using APIs or Programming with APIs, Instead of direct System Calls.


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System Call Sequence when Copying from One

File to another


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API Consider the ReadFile() function in the Win32 APIa function for reading from a file

Description of the parameters passed to ReadFile()

HANDLE filethe file to be read

LPVOID buffera buffer where the data will be read into and written fromDWORD bytesToReadthe number of bytes to be read into the buffer

LPDWORD bytesReadthe number of bytes read during the last read

LPOVERLAPPED ovlindicates if overlapped I/O is being used


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System Call Implementation Typically, a number associated with each system call

System-call interface maintains a table indexed according to these numbers

The system call interface invokes intended system call in OS kernel and returnsstatus of the system call and any return values

The caller need know nothing about how the system call is implemented

Just needs to obey API and understand what OS will do as a result call

Most details of OS interface hidden from programmer by API

Managed by run-time support library (set of functions built into librariesincluded with compiler)


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System Call Interface


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Example Windows/Unix system Call


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Types of System Calls Process Control

File Management

Device Management

Information Maintenance

Communications


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System Program Provide a convenient environment for program development and

execution

Some of them are simply user interfaces to system calls; others are

considerably more complex


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Standard C Library Example C program invoking printf() library call, which calls write() system call


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Operating System Design & Implementation

Important principle to separate

Policy: What will be done?

Mechanism: How to do it?

Mechanisms determine how to do something, policies decide what willbe done

The separation of policy from mechanism is a very important

principle, it allows maximum flexibility if policy decisions are to be

changed later


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Layered Approach The operating system is divided into a number of layers (levels), each

built on top of lower layers.

The bottom layer (layer 0), is the hardware; the highest (layer N) is the

user interface.

With modularity, layers are selected such that each uses functions

(operations) and services of only lower-level layers


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Layered View of Operating System


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Microkernel System Structure Moves as much from the kernel into user space

Communication takes place between user modules using messagepassing

Benefits:

Easier to extend a microkernel Easier to port the operating system to new architectures

More reliable (less code is running in kernel mode)

More secure

Detriments:

Performance overhead of user space to kernel space communication


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Virtual Machines Fundamental Idea behind a virtual machine is to abstract the hardware

of a single Computer into several different execution environments.

Illusion will be created that each separate execution environment is

running its own private computer.

The Operating System creates the illusion of multiple processes, each

executing on its own processor with its own (virtual) memory.

The virtual-machine concept provides complete protection of system

resources since each virtual machine is isolated from all other virtual

machines.


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VMware Architecture


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BIOS


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Motherboard BIOS


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System Boot

Operating system must be made available to hardware so hardware can

start it

Small piece of code bootstrap loader, locates the kernel, loads it

into memory, and starts it

Sometimes two-step process where boot block at fixed location

loads bootstrap loader

When power initialized on system, execution starts at a fixed

memory location

Firmware used to hold initial boot code


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Booting Steps

Power On the Computer Machine. NO Data to process for the Processor.

Data present in BIOS ROM will be processed first.

Perform POST.

Display System Settings.

Load Interrupt Handler and Device Drivers. Check CMOS for custom settings.

Initiate the Bootstrap sequence.

Searching for target BOOT drive.

Locate the MBR .

Start OS.


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Thnx

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2-systemstructure-110817130451-phpapp02.pdf