Chapter 1: Introduction
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What is an Operating System?
Batch Systems
Time Sharing Systems
Personal Computer Systems
Parallel or Multiprocessor Systems
Distributed Systems
Real -Time Systems
Handheld Systems
What is an Operating System?
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A program that acts as an intermediary between a user of
a computer and the computer hardware (manages a
computer’s hardware).
 Provides an environment in which a user can execute
programs
 Operating system is an interface between user and
hardware, between application program and hardware
and between two programs.
 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.
Computer System Components
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Computer system can be divided into four components
(see next slide):
 Hardware – provides basic computing resources
 CPU, memory, I/O devices
 Operating system
 Controls and coordinates use of hardware among
various applications and users (e.g. Windows, Linux)
 Application programs – define the ways in which the system
resources are used to solve the computing problems of the
users
 Word processors, compilers(C, C++, Java), web
browsers, database systems, video games
 Users
 People, machines, other computers
Abstract View of System Components
Operating System Definitions
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OS is a resource allocator
 Manages and allocates all resources (CPU time, memory
space, file-storage space, I/O devices, etc.)
 Decides between conflicting requests for efficient and fair
resource use
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OS is a control program
 Controls execution of programs to prevent errors and improper
use of the computer (control operations of I/O devices)
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Parts of the OS
 The one program running at all times on the computer is the
kernel.
 Shell – Operating systems such as Windows and Unix include
a command interpreter as a special program. It is an interface
between user and the kernel which can also be used to start an
application program. Graphical User Interface (GUI) is an
alternative interface for the OS.
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Everything else is either
 a system program (ships with the operating system), or
 an application program.
Kernel Services
 I/O Management
 Process Management
 Memory Management
 File Systems Management
 Device Drivers Management
 System Calls (Application Program Interface)
 Interprocess Communication
 Protection System
 Networking
Computer Startup
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Small piece of code – bootstrap program is
loaded at power-up or reboot
 Typically stored in ROM or EEPROM (electrically
erasable programmable ROM), generally known as
firmware
 Initializes all aspects of system
 Loads operating system kernel and starts execution
Computer System Organization
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Modern general purpose Computer-system consist of
 One or more CPUs, device controllers (disk controller, USB
controller, memory controller, etc.) connected through
common bus providing access to shared memory
 CPU and the device controllers can execute in parallel
(concurrently), competing for memory cycles
 Memory controller synchronizes access to the memory to
ensure orderly accessing
memory controller
Simple Batch Systems
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A fairly simple operating system was
used. An operator other than the
user was used.
 A card reader was used as input
device. CPU is generally idle due to
low speeds of mechanical I/O
devices compared to those of
electronic ones (e.g. slow punch
card reader).
 Processing speed is increased by
batching similar jobs together and
run them as a group.
 Automatic job sequencing allows
transfer of control from one job to
another.
Spooling
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Spooling: Simultaneous Peripheral Operation on-line
 Jobs are not read directly into memory but onto the disk.
Since reading is time consuming, some other jobs can be
performed during reading.
 Overlap I/O of one job with computation of another job.
While executing one job, the OS:
 Reads next job from card reader into a storage area on the
disk (job queue).
 Outputs printout of previous job from disk to printer
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The main goal is to reduce CPU idle time, since I/O speed
is slower than CPU speed
 By spooling technique a printer could be used by users
without waiting
Multiprogrammed Batch Systems
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Several jobs are kept in main
memory at the same time which is
known as job pool.
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The operating system picks one
job from memory to execute.
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When a job has to wait(e.g. for an
input), operating system switches
to another job.
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Eventually, the first job finishes
waiting and gets the CPU back.
OS Features Needed for Multiprogramming
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In multiprogramming systems there are several jobs in memory
at the same time.
 When the operating system selects a job from the job pool, it
loads that job into memory for execution.
 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
Memory management – the system must allocate the memory
to several jobs.
 CPU scheduling – the system must choose among several
ready to run jobs. The system must know their exact locations
in memory.
 Management of devices - including allocation , disk storage
and memory management.
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Time-Sharing (multitasking) Systems–Interactive
Computing
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A time-shared OS uses CPU scheduling and multiprogramming
that provides each user a small portion of time.
The CPU is multiplexed among several jobs that are kept in
memory and on disk (the CPU is allocated to a job only if the
job is in memory).
The CPU is switched among multiple jobs so frequently that the
users may interact with each program during execution.
A job swapped in and out of memory to the disk.
On-line communication between the user and the system is
provided
Time-sharing also compensates for low-speed I/O operations
such as low-speed keyboard typing.
A time-shared operating system allows many users to share the
computer simultaneously (multiuser).
Note: A program loaded into memory and executing is called a
process, job or task (will be explained later).
Personal Computer Systems
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Personal computers – computer system dedicated to a
single user.
I/O devices – keyboards, mice, display screens, small
printers.
Can adopt technology developed for larger operating
system (different technologies can be adapted).
May run several different types of operating systems
(Windows, MacOS, UNIX, Linux)
Client PCs, printers, servers
Parallel or Multiprocessor Systems
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Multiprocessor systems have more than one CPU in
close communication.
 Tightly coupled system – processors share memory and
other resources; communication usually takes place
through the shared memory.
 Advantages of parallel systems:
 Increased throughput: More work is done in the same time
period. Increasing processors by n does not mean
decreasing operation time by n.
 Economical: Shared peripherals and power supplies.
Several programs can be run on same set of data on a
shared disk
 Increased reliability
• fail-soft systems. The failure of one processor does not
halt the system. The rest continues to do the task
• graceful degradation: The ability to continue providing
service proportional to the level of surviving hardware.
Parallel Systems (Cont.)
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Asymmetric multiprocessing
 Each processor is assigned a specific task; master
processor schedules and allocates work to slave
processors.
 More common in extremely large systems
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Symmetric multiprocessing (SMP)
 Each processor performs all tasks within the operating
system
 All proccesors are peers, no mater-slave reationship
 Most modern operating systems support SMP
Symmetric Multiprocessing Architecture
multiple chips with single core
(single core on the chip)
A Dual-Core Design
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Multiple computing cores on a single chip - multicore
More efficient than multiple chips with single core because onchip communication is faster than between-chip
communication
Figure shows dual-core design with two cores on the same chip
Distributed Systems
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Distribute the computation among several physical
processors referred to as sites, nodes, computers etc.
 Unlike tightly-coupled parallel systems, these are Loosely
coupled systems
 each processor has its own local memory
 processors communicate with one another through various
communications lines, such as high-speed buses or
telephone lines.
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Advantages of distributed systems(DS).
 Resources Sharing (printers, files etc.)
 Computation speed up – load sharing (if there is an
overloading on a site)
 Reliability (if one site fails in a DS, the remaining sites can
potentially continue operating)
 Communications – information exchange
Distributed Systems (cont)
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Requires networking infrastructure.
 Collection of separate, possibly heterogeneous, systems
networked together
 Network is a communications path, TCP/IP is most
common
 Personal Area Network (PAN)
 Local Area Network (LAN)
 Metropolitan Area Network (MAN)
 Wide Area Network (WAN)
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Internet
 Communication scheme allows systems to exchange
messages
 Illusion of a single system
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Distributed systems may be either
 client-server systems or
 peer-to-peer systems
Distributed System StructuresGeneral Structure of Client-Server
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Client-Server Computing
 Clients: PCs and mobile devices
 Servers: Systems responding to requests generated by clients
 Compute-server system provides an interface to which a
client may send a request to perform an action (e.g.
database)
 File-server system provides interface for clients to store
and retrieve files (webserver)
Peer-to-Peer Computing
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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
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Examples include Napster and Gnutella,
Voice over IP (VoIP) such as Skype. It
allows clients to make voice calls and
video calls and to send text messages
over the Internet.
Real-Time Embedded Systems
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Embedded systems run real-time operating systems. Generally
there is no user interface. They perform managing and monitoring
of the hardware.
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Real-time systems often used as a control device in a dedicated
application such as controlling scientific experiments, medical
imaging systems, industrial control systems, and some
display systems (car engines, manufacturing robots, DVDs,
microwave ovens, firewalls,etc.) with little or no user interface
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Real-time OS has well-defined fixed time constraints
 Processing must be done within the defined constraint(in small
time interval). Data brought by sensors to the computer, must
be analyzed and corresponding control adjustments must be
done in a small time interval
 Correct operation only if constraints met
Mobile Systems
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Personal Digital Assistants (PDAs)
Handheld smartphones, tablets, etc
Use IEEE 802.11 wireless, or cellular data networks for
connectivity
Leaders are Apple iOS and Google Android
Issues:
 Limited memory
 Slow processors
 Small display screens.
History of Operating Systems
First Generation:
*1945-1955
*Vacuum Tubes
*OS: Plugboards
Second Generation:
*1955-1965
*Transistors
*OS: Batch Systems
Third Generation:
*1965-1980
*Integrated circuits
*OS: Multiprogramming
Fourth Generation:
*1980-present
*Large scale integration
*Personal computers
*OS: personal systems
Next Generation:
*????
*System connected to high
speed networks
*Wide area resource control
*OS: net-centric computing,
embedded systems.