Unit 1.Operating system. Introduction ppt

Silberschatz, Galvin and Gagne ©2018
Operating System Concepts – 10h
Edition
Chapter 1: Introduction

1.2 Silberschatz, Galvin and Gagne ©2018
Operating System Concepts – 10th
Edition
Objectives
 Describe the general organization of a computer system and the role
of interrupts
 Describe the components in a modern, multiprocessor computer
system
 Illustrate the transition from user mode to kernel mode
 Discuss how operating systems are used in various computing
environments
 Provide examples of free and open-source operating systems

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What is an Operating System?
 A program that acts as an intermediary between a user of a
computer and the computer hardware
 Operating system goals:
• Execute user programs and make solving user problems
easier
• Make the computer system convenient to use
• Use the computer hardware in an efficient manner

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Computer System Structure
 Computer system can be divided into four components:
• Hardware – provides basic computing resources
 CPU, memory, I/O devices
• Operating system
 Controls and coordinates use of hardware among various
applications and users
• Application programs – 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

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Abstract View of Components of Computer

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What Operating Systems Do
 Depends on the point of view
 Users want convenience, ease of use and good performance
• Don’t care about resource utilization
 But shared computer such as mainframe or minicomputer must keep
all users happy
• Operating system is a resource allocator and control program
making efficient use of HW and managing execution of user
programs
 Users of dedicate systems such as workstations have dedicated
resources but frequently use shared resources from servers
 Mobile devices like smartphones and tables are resource poor, optimized
for usability and battery life
• Mobile user interfaces such as touch screens, voice recognition
 Some computers have little or no user interface, such as embedded
computers in devices and automobiles
• Run primarily without user intervention

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Defining Operating Systems
 Term OS covers many roles
• Because of myriad designs and uses of OSes
• Present in toasters through ships, spacecraft, game machines,
TVs and industrial control systems
• Born when fixed use computers for military became more
general purpose and needed resource management and
program control

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Operating System Definition
 No universally accepted definition
 “Everything a vendor ships when you order an operating system” is a
good approximation
• But varies wildly
 “The one program running at all times on the computer” is the kernel, part
of the operating system
 Everything else is either
• A system program (ships with the operating system, but not part of
the kernel) , or
• An application program, all programs not associated with the
operating system
 Today’s OSes for general purpose and mobile computing also include
middleware – a set of software frameworks that provide addition services
to application developers such as databases, multimedia, graphics

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Overview of Computer System Structure

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Computer System Organization
 Computer-system operation
• One or more CPUs, device controllers connect through common
bus providing access to shared memory
• Concurrent execution of CPUs and devices competing for memory
cycles

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Computer-System Operation
 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
 Each device controller type has an operating system device driver
to manage it
 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

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Common Functions of Interrupts
 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

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Interrupt Timeline

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Interrupt-drive I/O Cycle

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I/O Structure
 Two methods for handling I/O
• After I/O starts, control returns to user program only
upon I/O completion
• After I/O starts, control returns to user program without
waiting for I/O completion

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Computer Startup
 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

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Storage Structure

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Storage Structure
 Main memory – only large storage media that the CPU can
access directly
• Random access
• Typically volatile
• Typically random-access memory in the form of Dynamic
Random-access Memory (DRAM)
 Secondary storage – extension of main memory that provides
large nonvolatile storage capacity

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Storage Structure (Cont.)
 Hard Disk Drives (HDD) – rigid metal or glass platters covered
with magnetic recording material
• Disk surface is logically divided into tracks, which are subdivided
into sectors
• The disk controller determines the logical interaction between the
device and the computer
 Non-volatile memory (NVM) devices– faster than hard disks,
nonvolatile
• Various technologies
• Becoming more popular as capacity and performance increases,
price drops

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Storage Definitions and Notation Review
The basic unit of computer storage is the bit . A bit can contain one of two
values, 0 and 1. All other storage in a computer is based on collections of bits.
Given enough bits, it is amazing how many things a computer can represent:
numbers, letters, images, movies, sounds, documents, and programs, to name
a few. A byte is 8 bits, and on most computers it is the smallest convenient
chunk of storage. For example, most computers don’t have an instruction to
move a bit but do have one to move a byte. A less common term is word,
which is a given computer architecture’s native unit of data. A word is made
up of one or more bytes. For example, a computer that has 64-bit registers and
64-bit memory addressing typically has 64-bit (8-byte) words. A computer
executes many operations in its native word size rather than a byte at a time.
Computer storage, along with most computer throughput, is generally
measured and manipulated in bytes and collections of bytes. A kilobyte , or
KB , is 1,024 bytes; a megabyte , or MB , is 1,0242
bytes; a gigabyte , or GB , is
1,0243
bytes; a terabyte , or TB , is 1,0244
bytes; and a petabyte , or PB , is 1,0245
bytes. Computer manufacturers often round off these numbers and say that
a megabyte is 1 million bytes and a gigabyte is 1 billion bytes. Networking
measurements are an exception to this general rule; they are given in bits
(because networks move data a bit at a time).

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Storage Hierarchy
 Storage systems organized in hierarchy
• Speed
• Cost
• Volatility
 Caching – copying information into faster storage system; main
memory can be viewed as a cache for secondary storage
 Device Driver for each device controller to manage I/O
• Provides uniform interface between controller and kernel

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Storage-Device Hierarchy

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How a Modern Computer Works
A von Neumann architecture

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Operating-System Operations
 Bootstrap program – simple code to initialize the system, load the
kernel
 Kernel loads
 Starts system daemons (services provided outside of the kernel)
 Kernel interrupt driven (hardware and software)
• Hardware interrupt by one of the devices
• Software interrupt (exception or trap):
 Software error (e.g., division by zero)
 Request for operating system service – system call
 Other process problems include infinite loop, processes
modifying each other or the operating system

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Multiprogramming (Batch system)
 Single user cannot always keep CPU and I/O devices busy
 Multiprogramming organizes jobs (code and data) so CPU
always has one to execute
 A subset of total jobs in system is kept in memory
 One job selected and run via job scheduling
 When job has to wait (for I/O for example), OS switches to
another job

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Multitasking (Timesharing)
 A logical extension of Batch systems– the CPU switches jobs 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

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Distributed Systems
 Distributed computiing
• Collection of separate, possibly heterogeneous, systems
networked together
 Network is a communications path, TCP/IP most common
– Local Area Network (LAN)
– Wide Area Network (WAN)
– Metropolitan Area Network (MAN)
– Personal Area Network (PAN)
• Network Operating System provides features between systems
across network
 Communication scheme allows systems to exchange
messages
 Illusion of a single system

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Memory Layout for Multiprogrammed System

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Dual-mode Operation
 Dual-mode operation allows OS to protect itself and other
system components
• User mode and kernel mode
 Mode bit provided by hardware
• Provides ability to distinguish when system is running user
code or kernel code.
• When a user is running  mode bit is “user”
• When kernel code is executing  mode bit is “kernel”
 How do we guarantee that user does not explicitly set the mode
bit to “kernel”?
• System call changes mode to kernel, return from call resets
it to user
 Some instructions designated as privileged, only executable in
kernel mode

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Transition from User to Kernel Mode

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Timer
 Timer to prevent infinite loop (or process hogging resources)
• Timer is set to interrupt the computer after some time period
• Keep a counter that is decremented by the physical clock
• Operating system set the counter (privileged instruction)
• When counter zero generate an interrupt
• Set up before scheduling process to regain control or terminate
program that exceeds allotted time

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Process Management
 A process is a program in execution. It is a unit of work within the
system. Program is a passive entity; process is an active entity.
 Process needs resources to accomplish its task
• CPU, memory, I/O, files
• Initialization data
 Process termination requires reclaim of any reusable resources
 Single-threaded process has one program counter specifying location
of next instruction to execute
• Process executes instructions sequentially, one at a time, until
completion
 Multi-threaded process has one program counter per thread
 Typically system has many processes, some user, some operating
system running concurrently on one or more CPUs
• Concurrency by multiplexing the CPUs among the processes /
threads

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Process Management Activities
 Creating and deleting both user and system processes
 Suspending and resuming processes
 Providing mechanisms for process synchronization
 Providing mechanisms for process communication
 Providing mechanisms for deadlock handling
The operating system is responsible for the following activities in
connection with process management:

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Memory Management
 To execute a program all (or part) of the instructions must be in
memory
 All (or part) of the data that is needed by the program must be in
memory
 Memory management determines what is in memory and when
• Optimizing CPU utilization and computer response to users
 Memory management activities
• Keeping track of which parts of memory are currently being used
and by whom
• Deciding which processes (or parts thereof) and data to move into
and out of memory
• Allocating and deallocating memory space as needed

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File-system Management
 OS provides uniform, logical view of information storage
• Abstracts physical properties to logical storage unit - file
• Each medium is controlled by device (i.e., disk drive, tape drive)
 Varying properties include access speed, capacity, data-
transfer rate, access method (sequential or random)
 File-System management
• Files usually organized into directories
• Access control on most systems to determine who can access
what
• OS activities include
 Creating and deleting files and directories
 Primitives to manipulate files and directories
 Mapping files onto secondary storage
 Backup files onto stable (non-volatile) storage media

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Mass-Storage Management
 Usually disks used to store data that does not fit in main
memory or data that must be kept for a “long” period of time
 Proper management is of central importance
 Entire speed of computer operation hinges on disk subsystem
and its algorithms
 OS activities
• Mounting and unmounting
• Free-space management
• Storage allocation
• Disk scheduling
• Partitioning
• Protection

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Caching
 Important principle, performed at many levels in a computer
(in hardware, operating system, software)
 Information in use copied from slower to faster storage
temporarily
 Faster storage (cache) checked first to determine if
information is there
• If it is, information used directly from the cache (fast)
• If not, data copied to cache and used there
 Cache smaller than storage being cached
• Cache management important design problem
• Cache size and replacement policy

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Characteristics of Various Types of Storage
Movement between levels of storage hierarchy can be explicit or implicit

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Migration of data “A” from Disk to Register
 Multitasking environments must be careful to use most recent value,
no matter where it is stored in the storage hierarchy
 Multiprocessor environment must provide cache coherency in
hardware such that all CPUs have the most recent value in their
cache
 Distributed environment situation even more complex
• Several copies of a datum can exist
• Various solutions covered in Chapter 19

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I/O Subsystem
 One purpose of OS is to hide peculiarities of hardware devices from
the user
 I/O subsystem responsible for
• Memory management of I/O including buffering (storing data
temporarily while it is being transferred), caching (storing parts of
data in faster storage for performance), spooling (the overlapping
of output of one job with input of other jobs)
• General device-driver interface
• Drivers for specific hardware devices

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Protection and Security
 Protection – any mechanism for controlling access of processes or
users to resources defined by the OS
 Security – defense of the system against internal and external attacks
• Huge range, including denial-of-service, worms, viruses, identity
theft, theft of service
 Systems generally first distinguish among users, to determine who can
do what
• User identities (user IDs, security IDs) include name and
associated number, one per user
• User ID then associated with all files, processes of that user to
determine access control
• Group identifier (group ID) allows set of users to be defined and
controls managed, then also associated with each process, file
• Privilege escalation allows user to change to effective ID with
more rights

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Virtualization
 Allows operating systems to run applications within other OSes
• Vast and growing industry
 Emulation used when source CPU type different from target type (i.e.
PowerPC to Intel x86)
• Generally slowest method
• When computer language not compiled to native code –
Interpretation
 Virtualization – OS natively compiled for CPU, running guest OSes
also natively compiled
• Consider VMware running WinXP guests, each running
applications, all on native WinXP host OS
• VMM (virtual machine Manager) provides virtualization services

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Virtualization (cont.)
 Use cases involve laptops and desktops running multiple OSes for
exploration or compatibility
• Apple laptop running Mac OS X host, Windows as a guest
• Developing apps for multiple OSes without having multiple systems
• Quality assurance testing applications without having multiple
systems
• Executing and managing compute environments within data
centers
 VMM can run natively, in which case they are also the host
• There is no general-purpose host then (VMware ESX and Citrix
XenServer)

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Computing Environments - Virtualization

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Computer System Architecture

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Computer-System Architecture
 Most systems use a single general-purpose processor
• Most systems have special-purpose processors as well
 Multiprocessors systems growing in use and importance
• Also known as parallel systems, tightly-coupled systems
• Advantages include:
1. Increased throughput
2. Economy of scale
3. Increased reliability – graceful degradation or fault tolerance
• Two types:
1. Asymmetric Multiprocessing – each processor is assigned
a specie task.
2. Symmetric Multiprocessing – each processor performs all
tasks

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Symmetric Multiprocessing Architecture

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Dual-Core Design
 Multi-chip and multicore
 Systems containing all chips
• Chassis containing multiple separate systems

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Non-Uniform Memory Access System

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Clustered Systems
 Like multiprocessor systems, but multiple systems working together
• Usually sharing storage via a storage-area network (SAN)
• Provides a high-availability service which survives failures
 Asymmetric clustering has one machine in hot-standby mode
 Symmetric clustering has multiple nodes running applications,
monitoring each other
• Some clusters are for high-performance computing (HPC)
 Applications must be written to use parallelization
• Some have distributed lock manager (DLM) to avoid conflicting
operations

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Clustered Systems

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Real-Time Embedded Systems
 Real-time embedded systems most prevalent form of computers
• Vary considerable, special purpose, limited purpose OS, real-time
OS
• Use expanding
 Many other special computing environments as well
• Some have OSes, some perform tasks without an OS
 Real-time OS has well-defined fixed time constraints
• Processing must be done within constraint
• Correct operation only if constraints met

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Operating-System Services

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Operating System Services
 Operating systems provide an environment for execution of programs
and services to programs and users
 One set of operating-system services provides functions that are
helpful to the user:
• User interface - Almost all operating systems have a user
interface (UI).
 Varies between Command-Line (CLI), Graphics User
Interface (GUI), touch-screen, Batch
• Program execution - The system must be able to load a program
into memory and to run that program, end execution, either
normally or abnormally (indicating error)
• I/O operations - A running program may require I/O, which may
involve a file or an I/O device
• File-system manipulation - The file system is of particular
interest. Programs need to read and write files and directories,
create and delete them, search them, list file Information,
permission management.

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Operating System Services (Cont.)
 One set of operating-system services provides functions that are
helpful to the user (Cont.):
• Communications – Processes may exchange information, on the
same computer or between computers over a network
 Communications may be via shared memory or through
message passing (packets moved by the OS)
• Error detection – OS needs to be constantly aware of possible
errors
 May occur in the CPU and memory hardware, in I/O devices, in
user program
 For each type of error, OS should take the appropriate action to
ensure correct and consistent computing
 Debugging facilities can greatly enhance the user’s and
programmer’s abilities to efficiently use the system

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Operating System Services (Cont.)
 Another set of OS functions exists for ensuring the efficient operation of
the system itself via resource sharing
• Resource allocation - When multiple users or multiple jobs
running concurrently, resources must be allocated to each of them
 Many types of resources - CPU cycles, main memory, file
storage, I/O devices.
• Logging - To keep track of which users use how much and what
kinds of computer resources
• Protection and security - The owners of information stored in a
multiuser or networked computer system may want to control use of
that information, concurrent processes should not interfere with
each other
 Protection involves ensuring that all access to system
resources is controlled
 Security of the system from outsiders requires user
authentication, extends to defending external I/O devices from
invalid access attempts

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A View of Operating System Services

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System Calls
 Programming interface to the services provided by the OS
 Typically written in a high-level language (C or C++)
 Mostly accessed by programs via a high-level Application
Programming Interface (API) rather than direct system call use
 Three most common APIs are Win32 API for Windows, POSIX API for
POSIX-based systems (including virtually all versions of UNIX, Linux,
and Mac OS X), and Java API for the Java virtual machine (JVM)
Note that the system-call names used throughout this text are generic

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Example of System Calls
 System call sequence to copy the contents of one file to another file

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Example of Standard API

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System Call Implementation
 Typically, a number is associated with each system call
• System-call interface maintains a table indexed according to
these numbers
 The system call interface invokes the intended system call in OS
kernel and returns status 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
libraries included with compiler)

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API – System Call – OS Relationship

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System Call Parameter Passing
 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

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Parameter Passing via Table

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Types of System Calls
 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

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 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
Types of System Calls (Cont.)

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 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

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 Protection
• Control access to resources
• Get and set permissions
• Allow and deny user access

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Examples of Windows and Unix System Calls

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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 and
Implementation

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Policy and Mechanism
 Policy: What needs to be done?
• Example: Interrupt after every 100 seconds
 Mechanism: How to do something?
• Example: timer
 Important principle: separate policy from mechanism
 The separation of policy from mechanism is a very
important principle, it allows maximum flexibility if policy
decisions are to be changed later.
• Example: change 100 to 200

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Implementation
 Much variation
• Early OSes in assembly language
• Then system programming languages like Algol, PL/1
• Now C, C++
 Actually usually a mix of languages
• Lowest levels in assembly
• Main body in C
• Systems programs in C, C++, scripting languages like PERL,
Python, shell scripts
 More high-level language easier to port to other hardware
• But slower
 Emulation can allow an OS to run on non-native hardware

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Operating System Structure
 General-purpose OS is very large program
 Various ways to structure ones
• Simple structure – MS-DOS
• More complex – UNIX
• Layered – an abstraction
• Microkernel – Mach

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Monolithic Structure – Original UNIX
 UNIX – limited by hardware functionality, the original UNIX operating
system had limited structuring.
 The UNIX OS consists of two separable parts
• Systems programs
• The kernel
 Consists of everything below the system-call interface and
above the physical hardware
 Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a large
number of functions for one level

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Traditional UNIX System Structure
Beyond simple but not fully layered

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Linux System Structure
Monolithic plus modular design

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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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Microkernels
 Moves as much from the kernel into user space
 Mach is an example of microkernel
• Mac OS X kernel (Darwin) partly based on Mach
 Communication takes place between user modules using
message passing
 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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Microkernel System Structure

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Modules
 Many modern operating systems implement loadable kernel
modules (LKMs)
• Uses object-oriented approach
• Each core component is separate
• Each talks to the others over known interfaces
• Each is loadable as needed within the kernel
 Overall, similar to layers but with more flexible
• Linux, Solaris, etc

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Hybrid Systems
 Most modern operating systems are not one pure model
• Hybrid combines multiple approaches to address performance,
security, usability needs
• Linux and Solaris kernels in kernel address space, so monolithic,
plus modular for dynamic loading of functionality
• Windows mostly monolithic, plus microkernel for different
subsystem personalities
 Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa programming
environment
• Below is kernel consisting of Mach microkernel and BSD Unix
parts, plus I/O kit and dynamically loadable modules (called
kernel extensions)

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macOS and iOS Structure

Unit 1.Operating system. Introduction ppt

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