operating system basics including mac os

Department of
Computer Science and Engineering
OPERATING SYSTEMS
School of Computing
Vel Tech Rangarajan Dr. Sagunthala R&D Institute of
Science and Technology
Faculty Name : P.GIRIJA
UNIT - 1

Department of Computer Science and Engineering
Course Content
2
UNIT I OPERATING SYSTEMS OVERVIEW 9
 Operating system overview: Objectives
 Functions
 Computer System Organization
 Operating System Structure
 Operating System Operations
 System Calls
 System Programs

Learning Resources
3
and Project
Management
(SEPM)
Text Books
1. Abraham Silberschatz, Peter Baer Galvin and Greg Gagne, “Operating System Concepts”, 9th
Edition, John Wiley and Sons Inc., 2012.
2.Richard Petersen, “Linux: The Complete Reference”, 6th Edition, Tata McGraw-Hill, 2008.
Reference Books
1. Andrew S. Tanenbaum, “Modern Operating Systems”, 4th Edition, Prentice Hall, Wesley,
2014.
2.William Stallings, “Operating Systems – Internals and Design Principles”, 7th Edition,
Prentice Hall, 2011.
3.Harvey M. Deitel, “Operating Systems”, 7th Edition, Prentice Hall, 2003.
4.D M Dhamdhere, “Operating Systems: A Concept-Based Approach”, 2nd Edition, Tata
McGraw-Hill Education, 2007.
5.Charles Crowley, “Operating Systems: A Design-Oriented Approach”, Tata McGraw Hill
Education”, 1996.
Digital Resources
1.http://www.tutorialspoint.com/operating_system/
2.http://www.mu.ac.in/myweb_test/MCA%20study%20material/OS%20-%20PDF.pdf
3.http://codex.cs.yale.edu/avi/os-book/OS8/os8c/slide-dir/PDF-dir/ch2.pdf
4.http://www.freebookcentre.net/CompuScience/Free-Operating-Systems-Books-download.html
/

Why you need to learn os?
4
and Project
Management
(SEPM)
 OS is a key part of a computer system
 It is the most important software that runs on a computer. It
manages the computer’s
 Memory
 Processes
 Software
 Hardware.
 It also allows you to communicate with the computer.

• An Operating System (OS) is an interface between a computer
user and computer hardware.
• An operating system ( OS) is system software that manages
computer hardware and software resources, and provides common
services for computer programs .
• An operating system is a program that acts as an interface between the user and
the computer hardware and controls the execution of all kinds of programs.
5
OPERATING SYSTEMS - Definition

Memory Management
Processor Management
Device Management
File Management
Security
Control over system performance
Job accounting
Error detecting codes
Coordination between other software and users

• Execute user Program & make solving user problems easier.
• Make the computer System convenient to use.
• Use the computer hardware in an efficient manner.
Goals of an operating System

• Hardware
• Operating system
• Application programs
• Users
Four main components of Computer

• Hardware – provides basic computing resources
• CPU, memory, I/O devices
• Operating system
• Controls and coordinates use of hardware among various applications and users
• Define the ways in which the system resources are used to solve the computing
problems of the users
• Word processors, compilers, web browsers, database systems, video games
• Users
• People, machines, other computers
Computer system can be divided into four components:

Views of Operating Systems

• Bootstrap program is loaded at power-up or reboot
• Typically stored in ROM or EPROM, generally known as
firmware
• Initializes all aspects of system
• Loads operating system kernel and starts execution
Computer Start up

Computer System Organization

Computer System Organization
• Computer-system operation
• One or more CPUs, device controllers connect through common
bus providing access to shared memory
• I/O devices and the CPU can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• CPU moves data from/to main memory to/from local buffers
• I/O is from the device to local buffer of controller

• Device controller informs CPU that it has finished its operation by
causing an interrupt
• Interrupt transfers control to the interrupt service routine generally,
through the interrupt vector, which contains the addresses of all the
service routines
• Interrupt architecture must save the address of the interrupted
instruction
• A trap or exception is a software-generated interrupt caused either by
an error or a user request
• An operating system is interrupt driven
INTERRUPTS

INTERRUPTS

• The OS preserves the state of the CPU by storing registers and the
program counter
• Determines which type of interrupt has occurred:
polling
• The interrupt controller polls (send a signal out to) each device to
determine which one made the request
vectored - interrupt system
• Separate segments of code determine what action should be taken
for each type of interrupt
INTERRUPT HANDLING

INTERRUPT TIMELINE

STORAGE HIERARCHY

• Storage is the only one of many types of I/O devices within a computer.
• A large portion of OS code is dedicated to managing I/O
• Because of its importance of reliability & performance.
• Computer system consists of CPU & multiple devices controllers through
common bus.
• Each device controller is in charge of a specific types of devices.
I/O STRUCTURE

DEVICE CONTROLLER
• Maintains local buffer storage & set of Special purpose registers.
DEVICE DRIVER
• OS have a device driver for each device controller.
• Device driver understands the device controller & gives uniform interface
to the rest of the OS.
• Device controller transfers blocks of data from buffer storage directly to
main memory without CPU intervention
• Only one interrupt is generated per block, rather than the one interrupt per
byte.
I/O STRUCTURE

DEVICE CONTROLLER
CPU
ADDRESS BUS
DATA BUS
Registers Registers
LOCAL BUFFERS
MAIN MEMORY

• To start an IO operations ,device driver loads the appropriate registers within
the device controller.
• Device controller in turns examines the content of these registers to
determine what action to take.
• The controller starts the transfer of data from the device to its local buffer.
• Once the transfer of data is complete ,the device controller informs the device
driver via an interrupt that it has finished its operations.
• Device driver then return the control to OS.
Issue:
• This form of interrupt driven IO is fine for moving small amounts of data.
• But can produce high overhead when used for bulk data movement.
Working of I/O operations

DMA(DIRECT MEMORY ACCESS)
• To solve the above problem ,DMA is used.
• After setting up buffers, pointers & counters for IO devices, the
device controller transfers an entire block of data directly to or from
its own buffer storage to memory without intervention of CPU.
• Only one interrupt is generated per block, to tell the device driver
that the operation has completed.
• While the device controller is performing these operations , CPU is
available to accomplish other works.
Working of I/O operations

How a Modern Computer Works

OPERATING SYSTEM STRUCTURE
COMMONALITIES
MULTIPROGRAMMING
MULTI TASKING
(TIME SHARING)

• Multiprogramming (Batch system) needed for efficiency
• Capability of running multiple programs by the CPU.
• It increases CPU utilization by organizing jobs (code and data) so CPU
always has one to execute.
• Single program (user) cannot keep CPU and I/O devices busy at all times
• A subset of total jobs in system is kept in memory
• One job selected and run via job scheduling
• When it has to wait (for I/O for example), OS switches to another job
JOB
1
J
JOB
3
JOB
2
JOB
4
JOB POOL

• Timesharing (multitasking) is logical extension in which CPU
• switches occurs so frequently that users can interact with each job while it
is running, creating interactive computing
• Response time should be < 1 second
• Each user has at least one program executing in memory process
• If several jobs ready to run at the same time  CPU scheduling
• If processes don’t fit in memory, swapping moves them in and out to
run
• Virtual memory allows execution of processes not completely in
memory

• UNIX is a powerful Operating
System initially developed by
Ken Thompson, Dennis
Ritchie at AT&T Bell
laboratories in 1970.

• Features of UNIX Operating System

• Multitasking: A UNIX operating system is a multitasking operating system that allows you
to initiate more than one task from the same terminal so that one task is performed as a
foreground and the other task as a background process.
• Multi-user: UNIX operating system supports more than one user to access computer
resources like main memory, hard disk, tape drives, etc
• Portability: This feature makes the UNIX work on different machines and platforms with
the easy transfer of code to any computer system.
• File Security and Protection: Being a multi-user system, UNIX makes special consideration
for file and system security.
• Communication: In UNIX, communication is an excellent feature that enables the user to
communicate worldwide. It supports various communication facilities provided using the
write command, mail command, talk command, etc.
• Open Source: UNIX operating system is open source it means it is freely available to all
and is a community-based development project.
• Accounting: UNIX keeps an account of jobs created by the user.
• UNIX Tools and Utilities:like compiler ,interpreter...etc for unix grep,sed,awk etc...

• The structure of Unix OS Layers are as follows:

• Interrupt driven (hardware and software)
• Hardware interrupt by one of the devices
• Software interrupt (exception or trap):
• Software error (e.g., division by zero or invalid memory access)
• Request for operating system service
• For each type of interrupt separate segment of code in the OS
determine what action should be taken.
• ISR [Interrupt Service Routine] provided to deal with interrupt.
• A properly designed OS ensure that an incorrect or malicious program cannot
cause other programs to execute incorrectly.
Operating-System Operations

• Dual-mode operation allows OS to protect itself and other system components
2 MODES OF OPERATIONS
DUAL MODE & MULTI MODE OPERATIONS
User mode
kernel mode or Supervised
mode or privileged mode.

• Mode bit
• Added to hardware of the computer.
• To indicate the current mode
• Kernel (0)
• User (1)
• System executing a user application – User mode.
• User Application request a service from OS (via System call).
• System must translate from user mode to kernel mode to fulfill the
request.

• Hardware starts in kernel mode.
• OS is then loaded & starts user application in user mode.
• Whenever trap or interrupt occurs ,the hardware switches
from user mode to kernel mode.
• OS gains the control of computer in kernel mode.
• The system always switches to user mode before passing
control to a user program.
System Boot

• The hardware allows these instructions to be executed only
in kernel mode.
• Example:
• The instructions to switch to kernel mode.
• I/O control
• Timer management
• Interrupt management
Privileged Instructions(System Calls)

• CPU uses more than one bit to set & test the mode.
• CPU supports virtualization frequently have a separate mode to
indicate when the Virtual Machine Manager(VMM) & the
virtualization management software VMs is in control of the
system.
• VMM has more privileges than user processes but fewer than the
kernel.
• Example
• Intel 64 family of CPU supports 4 privileged levels & virtualization
but does not have separate mode for virtualization.
Beyond two modes[multi mode operations]

• Provides the user program to ask the operating system to perform tasks
reserved for the OS.
• It is invoked in variety of ways.
• Usually it takes the form of a trap to a specific location in the interrupt vector.
• Trap executed by a generic trap instruction ,syscall instruction to invoke a
system call.
• When system call is executed ,hardware treated it as software interrupt.
• Control passes through interrupt vector to a service routine & mode bit is set
to kernel mode.
• The kernel examines the interrupting instruction to determine what system
call has occurred.
SYSTEM CALL

• A parameter indicates what type of service the user program is
requesting.
• Additional information passed in registers, on the stack or in memory.
• Kernel verifies that parameters are correct & legal, execute the request
& returns control to the instruction following the system call.
No bit mode
• Lack of hardware supported with dual mode cause serious short
comings.
Example
• MS DOS – Intel Architecture has no mode bit & no dual mode.
Example for Dual mode
• Windows 10,UNIX, Linux
SYSTEM CALL

• Programming interface to the services provided by the OS.
• Typically written in a high-level language (C or C++)
SYSTEM CALLS
User Mode
Kernel
Mode

Examples - SYSTEM CALLS
• System call sequence to copy the contents of one file to another file

• Acquire input File name:
• To enter the file name
• 2 ways are there
• Through keyboard
• Mouse
• Frequently system execute thousands of system calls per second.
Examples - SYSTEM CALLS

• Specifies set of functions that are available to an application programmer,
including parameters passed to each functions & return values the
programmer can expect.
• Mostly accessed by programs via a high-level Application
Programming Interface (API) rather than direct system call .
•
SYSTEM CALLS - APIs

Examples of Standard APIs

• Why application programmer prefer programming according to API than
invoking system calls?
• Program portability
• Application programmer design a program using an API can expect her
program to compile & run on any system that supports the same API.
SYSTEM CALLS - APIs

• Many programming languages provides a system call interface.
• It serves as the link to system calls made available by operating system.
• It intercepts function calls in the API & invokes the necessary system call written
the OS.
• A number is associated with each system call.
• It maintains a table indexed according to these numbers.
• It invokes intended system call in OS kernel & returns status of the system calls &
any return values.
• The caller need know nothing about how the system call is implemented.
• Just need only obey the API & understand what OS will do as a result of system
call.
• Most detail of OS interface hidden from programmer by API.
• Managed by run time support library (set of functions built into libraries included
with compiler)
SYSTEM CALLS interface

API – System Call – OS Relationship

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

• Often, more information is required than simply identity of desired
system call
• Exact type and amount of information vary according to OS and call
• Three general methods used to pass parameters to the OS
• Simplest: pass the parameters in registers
• In some cases, may be more parameters than registers
• Parameters stored in a block, or table, in memory, and address of
block passed as a parameter in a register
• This approach taken by Linux and Solaris
• Parameters placed, or pushed, onto the stack by the program and
popped off the stack by the operating system
• Block and stack methods do not limit the number or length of
parameters being passed
SYSTEM CALLS Parameter passing

SYSTEM CALLS Parameter passing

• Process control
• create process, terminate process
• end, abort
• load, execute
• get process attributes, set process attributes
• wait for time
• wait event, signal event
• allocate and free memory
• Dump memory if error
• Debugger for determining bugs, single step execution
• Locks for managing access to shared data between processes
Types of System Calls

• File management
• create file, delete file
• open, close file
• read, write, reposition
• get and set file attributes
• Device management
• request device, release device
• read, write, reposition
• get device attributes, set device attributes
• logically attach or detach devices

• Information maintenance
• get time or date, set time or date
• get system data, set system data
• get and set process, file, or device attributes
• Communications
• create, delete communication connection
• send, receive messages if message passing model to host name or
process name
• From client to server
• Shared-memory model create and gain access to memory regions
• transfer status information
• attach and detach remote devices

Examples of Windows and Unix System Calls

SYSTEM PROGRAMS

• Provide a convenient environment for program development and
execution.
• Some of them are simply user interfaces to system calls;
• others are considerably more complex
• System programs are divided into following categories
• File manipulation
• Status information sometimes stored in a File modification
• Programming language support
• Program loading and execution
• Communications
• Background services
SYSTEM PROGRAMS- Definition

File management
• Create,
• delete,
• copy,
• rename,
• print,
• dump,
• list, and
• generally manipulate files and directories
SYSTEM PROGRAMS - Categories

Status information
• Ask the system for info
Simple information's
• date,
• time,
• amount of available memory,
• disk space,
• number of users
Complex information's
• Detailed performance,
• logging, and
• debugging information,etc.

File modification
• Several Text editors may be available to create and modify the
content of files stored on disk or other storage devices.
• Special commands to search contents of files or perform
transformations of the text

Programming-language support
• Compilers,
• assemblers,
• debuggers and
• Interpreters
• For some common programming languages (such as C,C++,JAVA ,Visual
Basic & PERL)
• Provided to the user with the operating system.

Program loading and execution
• Once a program is assembled or compiled , it must be loaded into
memory to be executed.
• Absolute loaders,
• Relocatable loaders,
• linkage editors, and
• overlay-loaders,
• Debugging systems for higher-level or machine language are needed.

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