Republic of Yemen

Ministry of Higher Education

‫الجمهورية اليمنية‬
and Scientific Research ‫وزارة التعليم العالي والبحث العلمي‬
Al-Rasheed Smart University ‫جامعة الرشيد الذكية‬

Chapter 1: Introduction

Operating System Concepts – 10h Edition Silberschatz, Galvin and Gagne ©2018
 Course Objectives

• To describe the basic organization of computer systems.

• To describe the services an operating system provides to users,
processes, and other systems.
• To discuss the various ways of structuring an operating system.
• To introduce the notion of a process and a thread.
• To introduce CPU scheduling, which is the basis for
multiprogrammed operating systems.
• To develop a description of deadlocks.
• To provide a detailed description of various ways of organizing
memory hardware.

Operating System Concepts – 10th Edition 1.2 Silberschatz, Galvin and Gagne ©2018
 Course Syllabus

• Introduction.
• Operating-System Structures.
• Processes.
• Threads.
• CPU Scheduling.
• Process Synchronization.
• Deadlocks.
• Main Memory Management.

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 Chapter 1: Outline
• Introduction.
• Computer System Structure.
• What is an Operating System?
• What Operating Systems Do?
• Computer System Organization.
• Storage Structure.
• Multiprocessing Architecture.
• Operating-System Operations.
• Protection and Security.
• Computing Environments.

Operating System Concepts – 10th Edition 1.4 Silberschatz, Galvin and Gagne ©2018
 Introduction

 A computer is an electronic device, operating under the

control of instructions stored in its own memory

Accepts Produces
data Processing information
(input) (output)

Page 4 5
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 Information Technology

Building Blocks of Information Technology

Hardware Software Network Data

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 TWO CATEGORIES OF SOFTWARE

1. Applications software
2. Support software

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 Computer System Structure (1/2)

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. Ex. Word processors, compilers, web
browsers, database systems, video games.
• Users
➢ People, machines, other computers

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 Computer System Structure (2/2)

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 What is an Operating System? (1/2)

• An operating system is a program that manages a

computer’s hardware. It also provides a basis for
application programs and acts as an intermediary
between the computer user and the computer hardware.

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 What is an Operating System? (2/2)

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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 What Operating Systems Do? (1/4)

User 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.

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 What Operating Systems Do? (2/4)

System View
• From the computer’s point of view, the operating system
is the program most intimately involved with the
hardware. In this context, we can view an operating
system as a resource allocator.
• A computer system has many resources that may be
required to solve a problem: CPU time, memory space,
file-storage space, I/O devices, and so on. The operating
system acts as the manager of these resources.

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 What Operating Systems Do? (3/4)

• OS is a resource allocator
➢ Manages all resources.
➢ 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.

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 What Operating Systems Do? (4/4)

• A more common definition, and the one that we usually

follow, is that the operating system is the one program
running at all times on the computer—usually called the
kernel.
• (Along with the kernel, there are two other types of
programs: system programs, which are associated with
the operating system but are not necessarily part of the
kernel, and application programs, which include all
programs not associated with the operation of the
system.)

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 Computer System Organization (1/3)

• A modern general-purpose computer system consists of

one or more CPUs and a number of device controllers
connected through a common bus that provides access to
shared memory.

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 Computer System Organization (2/3)

Computer Startup (1/2)

• bootstrap program is loaded at power-up or reboot
➢ Typically stored in ROM or electrically erasable
programmable read-only memory (EPROM), generally known
as firmware.

➢ Initializes all aspects of system.

➢ Loads operating system kernel and starts execution.

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 Computer System Organization (2/3)

Computer Startup (2/2)

©Ahmed Hagag Operating Systems 19

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 Computer System Organization (2/3)

Computer Startup (2/2)

©Ahmed Hagag Operating Systems 20

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 Computer System Organization (3/3)

Interrupts (1/2)
• The occurrence of an event is usually signaled by an
interrupt from either the hardware or the 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 a system call (also called a monitor call).
• Interrupts are an important part of a computer
architecture. Each computer design has its own interrupt
mechanism, but several functions are common.

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 Computer System Organization (3/3)

Interrupts (2/2)
• 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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 Storage Structure (1/4)

The basic unit of computer storage is the bit. A bit can contain one of two
Review 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
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 Structure (2/4)

• Main memory – only large storage media that the CPU

can access directly.
➢ Random access
➢ Typically volatile

• Secondary storage – extension of main memory that

provides large nonvolatile storage capacity.

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 Storage Structure (3/4)

• Hard 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.

• Solid-state disks – faster than hard disks, nonvolatile.

➢ Various technologies.
➢ Becoming more popular.

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 Storage Structure (4/4)

• Storage systems organized in hierarchy

➢ Speed
➢ Cost
➢ Volatility

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 How a Modern Computer Works

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 Multiprocessing Architecture (1/2)

• Multiprocessors systems growing in use and importance

➢ Also known as parallel systems.
➢ Advantages include:

1. Increased throughput: by increasing the number of processors, we expect

to get more work done in less time.

2. Economy of scale: Multiprocessor systems can cost less than equivalent

multiple single-processor systems, because they can share peripherals, mass
storage, and power supplies.

3. Increased reliability: graceful degradation or fault tolerance.

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 Multiprocessing Architecture (2/2)

• Multiprocessors systems growing in use and importance

➢ Two types:
1. Asymmetric Multiprocessing – each processor is assigned a specie task.
2. Symmetric Multiprocessing – each processor performs all tasks.

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 Multiprocessing Architecture (2/2)

• Multiprocessors systems growing in use and importance

➢ Two types:
1. Asymmetric Multiprocessing – each processor is assigned a specie task.
2. Symmetric Multiprocessing – each processor performs all tasks.

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 A Dual-Core Design

• Multi-chip and multicore

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 Operating-System Structure (1/3)

• Multiprogramming (Batch system) 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

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 Operating-System Structure (2/3)

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 Operating-System Structure (3/3)

• 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

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 Operating-System Operations (1/4)

• 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
➢ Other process problems include infinite loop, processes
modifying each other or the operating system

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 Operating-System Operations (2/4)

• Dual-mode operation allows OS to protect itself and

other system components
• User mode and kernel mode (also called supervisor
mode, system mode, or privileged mode).

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 Operating-System Operations (3/4)

• A bit, called the mode bit, is added to the hardware of

the computer to indicate the current mode: kernel (0) or
user (1).
➢ 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.

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 Operating-System Operations (4/4)

• Transition from User to Kernel Mode

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 Levels of Storage

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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, etc.

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 Computing Environments (1/9)

• The current trend is toward providing more ways to

access these computing environments.
• Companies establish portals, which provide Web
accessibility to their internal servers.
• Network computers (or thin clients) — which are
essentially terminals that understand web-based
computing — are used in place of traditional
workstations where more security or easier maintenance
is desired.
• Mobile computers interconnect via wireless networks.

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 Computing Environments (2/9)

• Distributed computing: 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.

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 Computing Environments (3/9)

• Client-Server Computing

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 Computing Environments (4/9)

• Peer-to-Peer

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 Computing Environments (5/9)

• Virtualization – is a technology that allows operating

systems to run as applications within other operating
systems.
• 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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 Computing Environments (6/9)

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 Computing Environments (7/9)

• VMware Architecture

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 Computing Environments (8/9)

• Cloud Computing – Delivers computing, storage, even

apps as a service across a network.
➢ Public cloud – available via Internet to anyone
willing to pay.
➢ Private cloud – run by a company for the
company’s own use.
➢ Hybrid cloud – includes both public and private
cloud components.

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 Computing Environments (9/9)

• Software as a Service (SaaS)

➢ One or more applications available via the Internet (i.e.,
word processor).
• Platform as a Service (PaaS)

➢ Software stack ready for application use via the Internet

(i.e., a database server).
• Infrastructure as a Service (IaaS)

➢ Servers or storage available over Internet (i.e., storage

available for backup use).

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 End of Chapter 1

Operating System Concepts – 10h Edition Silberschatz, Galvin and Gagne ©2018