Operating system- Chapter 1.pptx to study

1.2 A.V. Bernardo @DLSAU
Operating System
Chapter 1: Introduction
 What Operating Systems Do
 Computer-System Organization
 Computer-System Architecture
 Operating-System Structure
 Operating-System Operations
 Process Management
 Memory Management
 Storage Management
 Protection and Security
 Distributed Systems
 Special-Purpose Systems
 Computing Environments

Operating System
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.

Operating System
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

Operating System
Four Components of a Computer System

Operating System
Operating System Definition
 OS is a resource allocator
 Manages all resources and allocates them to specific
programs and users as necessary for their tasks.
 A computer system has many resources (hardware and
software) that may be required to solve problem: CPU time,
memory space, file storage space, I/O devices and so on.
 Decides between conflicting requests for efficient and fair
resource use
 OS is a control program
 Controls execution of programs to prevent errors and improper
use of the computer
 It is especially concerned with the operation and control of I/O
devices.

Operating System
Operating System Definition (Cont.)
 No universally accepted definition of what is part of the operating
system and what is not.
 “Everything a vendor ships when you order an operating system”
is good approximation
 “The one program running at all times on the computer” is the
kernel. Everything else is either a system program (ships with
the operating system) or an application program

Operating System
Computer Startup
 bootstrap program is loaded at power-up or rebooted
 Typically stored in ROM or EEPROM, generally known as
firmware
 It initializes all aspects of system, from CPU registers to device
controllers to memory contents
 Loads operating system kernel and starts execution
 The operating system then starts executing the first process,
such as “init”, and waits for some event to occur.
 The occurrence of an event is usually signaled by an interrupt
from either hardware or software.
 Hardware may trigger an interrupt at any time by sending a
signal to the CPU, usually by way of the system bus.
 Software may trigger an interrupt by executing a special
operation called system call(also called as monitor call)

Operating System
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
 To ensure orderly access to the shared memory , a memory controller
is provided whose function is to synchronize access to the memory.

Operating System
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.
 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.

Operating System
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 vector – indexed by a unique device number, given with
the interrupt request, to provide the address of the interrupt service
routine for the interrupting device.
 Interrupt architecture must save the address of the interrupted
instruction.
 Incoming interrupts are disabled while another interrupt is being
processed to prevent a lost interrupt.
 A trap is a software-generated interrupt caused either by an error
or a user request.
 An operating system is interrupt driven.

Operating System
Interrupt Handling
 The operating system preserves the state of the CPU by storing
registers and the program counter.
 Determines which type of interrupt has occurred:
 Polling- – the querying of all I/O devices to detect which
requested services
 vectored interrupt system.
 Separate segments of code determine what action should be taken
for each type of interrupt

Operating System
I/O Structure
 After I/O starts, control returns to user program only upon I/O
completion.
 Wait instruction idles the CPU until the next interrupt
 Wait loop (contention for memory access).
 At most one I/O request is outstanding at a time, no
simultaneous I/O processing.
 After I/O starts, control returns to user program without waiting
for I/O completion.
 System call – request to the operating system to allow user
to wait for I/O completion.
 Device-status table contains entry for each I/O device
indicating its type, address, and state.
 Operating system indexes into I/O device table to determine
device status and to modify table entry to include interrupt.

Operating System
 In the simplest case, the I/O is started; then, at I/O completion,
control is returned to the user process. This is known as
synchronous I/O.
 The other possibility ( asynchronous I/O) is to return control to the
user program without waiting for the I/O to complete.

Operating System
Two I/O Methods
Synchronous Asynchronous

Operating System
Two I/O methods a) interrupt –driven ,
b) DMA
 A user program, or the operating itself, may request data transfer.
 The operating systems finds a buffer( an empty buffer for input, a
full buffer for output) from a queue of buffers to transfer. ( A buffer
is typically 128-4096 bytes, depending on the device type).
 The DMA controller then has its registers set to the appropriate
source and destination addresses, and transfer length. This
register setting is usually done by a device driver, which knows
exactly how this information is to be provided to the controller.
 The DMA controller then instructed (via a control bits in a control
register) to start the I/O operation. Meanwhile the CPU has been
free to perform other tasks since it gave the transfer information to
the controller.
 The DMA controller interrupts the CPU when the transfer has been
completed.

Operating System
Device-Status Table

Operating System
Figure 2.3
 Each table entry indicates the device type, its address and its state(
not functioning, idle or busy).
 If the device is busy with a request, the type of request and other
parameters will be stored in the table entry for that device.
 Since it is possible for other processes to issue request to the
same device , we may have a list or chain of waiting requests.
 Thus, in addition to the I/O device table , an operating system may
have a request list for each device.

Operating System
Direct Memory Access Structure
 Used for high-speed I/O devices able to transmit information at
close to memory speeds.
 After setting up buffers, pointers, and counters for the I/O device,
the device controller transfers blocks of data from buffer storage
directly to main memory without CPU intervention.
 Only on interrupt is generated per block, rather than the one
interrupt per byte.

Operating System
Storage Structure
 Main memory – only large storage media that the CPU can access
directly.
 Secondary storage – extension of main memory that provides large
nonvolatile storage capacity.
 Magnetic disks – 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. The controller takes instructions
from the CPU and orders the disk drive to carry out the
instruction.

Operating System
Storage Hierarchy
 Storage systems organized in hierarchy.
 Speed
 Cost
 Volatility
 Caching – copying information into faster storage system; main
memory can be viewed as a last cache for secondary storage.

Operating System
Storage-Device Hierarchy

Operating System
 The wide variety of storage systems in a computer system can be
organized in a hierarchy according to their speed and their cost.
 The higher levels are expensive but are fast.
 As we move down the hierarchy , the cost per bit decreases,
whereas the access time increases.
 In hierarchy shown in the figure above, the storage systems above
disks is volatile, whereas the storage system below main memory
is nonvolatile.

Operating System
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

Operating System
Performance of Various Levels of Storage
 Movement between levels of storage hierarchy can be explicit or
implicit

Operating System
Migration of Integer A from Disk to Register
 Multitasking environments must be careful to use most recent
value, not 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 17

Operating System
Operating System Structure
 Multiprogramming needed for efficiency
 Single user cannot keep CPU and I/O devices busy at all times
 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 it has to wait (for I/O for example), OS switches to another job
 Timesharing (multitasking) is logical extension in which 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

Operating System
Memory Layout for Multiprogrammed System

Operating System
 Multiprogramming increases CPU utilization by organizing the job
so that the CPU always has something to execute.
 The operating system keeps several jobs in memory at a time(
figure above). This set of jobs is a subset of the jobs kept in the
pool.
 The OS picks and begins to execute one of the jobs in the memory.
 The job may have to wait for some task, such as a tape to be
mounted, a command to be typed on a keyboard , or an I/O
operation to complete.
 In a nonmultiprogrammed system, the CPU would sit idle,
 In multiprogramming system, the operating system simply switches
to and executes another job.
 When the job needs to wait , the CPU is switched to another job
and so on.

Operating System
Operating-System Operations
 Interrupt driven by hardware
 Software error or request creates exception or trap
 Division by zero, request for operating system service
 Other process problems include infinite loop, processes modifying
each other or the operating system
 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
 Some instructions designated as privileged, only
executable in kernel mode
 System call changes mode to kernel, return from call resets
it to user

Operating System
Transition from User to Kernel Mode
 Timer to prevent infinite loop / process hogging resources
 Set interrupt after specific period
 Operating system decrements counter
 When counter zero generate an interrupt
 Set up before scheduling process to regain control or terminate
program that exceeds allotted time

Operating System
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.
 A program is a passive entity such as the contents of the file stored on disk,
 A process is an active entity, with a program counter specifying the next
instruction to execute.
 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

Operating System
Process Management Activities
The operating system is responsible for the following activities in
connection with process management:
 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

Operating System
Memory Management
 All data in memory before and after processing
 All instructions in memory in order to execute
 Memory management determines what is in memory 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

Operating System
Storage Management
 OS provides uniform, logical view of information storage
 Abstracts physical properties to logical storage unit - file
a file is a collection of related information defined by its creator.
 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
- magnet tape, magnetic disk, and optical disk are the most common media.
 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

Operating System
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
 Free-space management
 Storage allocation
 Disk scheduling
 Some storage need not be fast
 Tertiary storage includes optical storage, magnetic tape
 Still must be managed
 Varies between WORM (write-once, read-many-times) and RW (read-
write)

Operating System
I/O Subsystem
 One purpose of OS is to hide peculiarities of hardware devices
from the user
 For example, in UNIX, the peculiarities of I/O devices are hidden
from the bulk of the operating systems itself by the I/O systems.
 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

Operating System
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

Operating System
Computing Environments
 Traditional computer
 Blurring over time
 Office environment
 PCs connected to a network, terminals attached to
mainframe or minicomputers providing batch and
timesharing
 Now portals allowing networked and remote systems
access to same resources
 Home networks
 Used to be single system, then modems
 Now firewalled, networked

Operating System
Computing Environments (Cont.)
 Client-Server Computing
 Dumb terminals supplanted by smart PCs
 Many systems now servers, responding to requests generated by
clients
 Compute-server provides an interface to client to request
services (i.e. database)
 File-server provides interface for clients to store and retrieve
files

Operating System
Peer-to-Peer Computing
 Another model of distributed system
 P2P does not distinguish clients and servers
 Instead all nodes are considered peers
 May each act as client, server or both
 Node must join P2P network
 Registers its service with central lookup service on network,
or
 Broadcast request for service and respond to requests for
service via discovery protocol
 Examples include Napster and Gnutella

Operating System
Web-Based Computing
 Web has become ubiquitous
 PCs most prevalent devices
 More devices becoming networked to allow web access
 New category of devices to manage web traffic among similar
servers: load balancers
 Use of operating systems like Windows 95, client-side, have
evolved into Linux and Windows XP, which can be clients and
servers

Operating system- Chapter 1.pptx to study

More Related Content

Similar to Operating system- Chapter 1.pptx to study (20)

Recently uploaded (20)

Operating system- Chapter 1.pptx to study