Applied Operating System
MODULE 1 – IT0035
WHAT IS AN OPERATING SYSTEM? ▪ Batch based interface
▪ Graphical User interface
An Operating System (OS) is a program or
2. Program Execution – The OS must have the
system software that acts as an interface between
capability to load a program into memory and
the user and the computer hardware and controls
execute that program.
the execution of all kinds of programs.
3. File System Manipulation – Programs need
It is not possible for the user to use any computer has to be read and then write them as files and
or mobile device without having an operating directories. File handling portion of OS also
system. allows users to create and delete files by
Goals of Operating System specific name along with extension, search for
a given file and / or list file information.
1. Execute user programs and make solving user
4. Input / Output Operations – A program
problems easier.
which is currently executing may require I/O,
2. Make the computer system convenient to use.
which may involve file or other I/O device. The
3. Use the computer hardware in an efficient
OS is responsible for reading and/or writing
manner.
data from I/O devices such as disks, tapes,
Components of a Computer System printers, keyboards, etc.
5. Communication – Process needs to swap
× Computer hardware
over information with other process.
→ CPU, memory and I/O devices, provides
Processes executing on same computer
the basic computing resources.
system or on different computer systems can
× Application programs
communicate using operating system
→ are used to solve the computing
support.
problems of the users such as word
6. Resource Allocation – The OS manages the
processors, games and business
different computer resources such as CPU
programs.
time, memory space, file storage space, I/O
× Users devices, etc. and allocates them to different
→ who utilize a computer or network application programs and users.
service trying to solve different 7. Error Detection – The operating system
problems. should be able to detect errors within the
× Operating Systems computer system (CPU, memory, I/O, or user
→ controls and coordinates the use of the program) and take the appropriate action.
hardware among the various application 8. Job Accounting – OS keeps track of time and
programs for the various users. resources used by various tasks and users, this
information can be used to track resource
COMMON SERVICES OFFERED BY ALMOST ALL
usage for a particular user or group of user.
OPERATING SYSTEMS:
9. Security and Protection – Protection is any
1. User Interface (UI) – Refers to the part of an mechanism for controlling access of
OS, or device that allows a user to enter and processes or users to resources defined by the
receive information. OS. Security is a defense of the system against
Types of UI: internal and external attacks (denial-of-
▪ Command Line Interface
Applied Operating System
MODULE 1 – IT0035
service, worms, viruses, identity theft, theft of occur so frequently. Thus, the user can
service) receive an immediate response. Response
time should be < 1 second
What is a Kernel? › Each user has at least one program
Kernel is the central part of an OS which manages executing in memory
system resources and is always resident in › If several jobs ready to run at the same
memory. It also acts like a bridge between time -> CPU scheduling
application and hardware of the computer. It is › If processes don’t fit in memory, swapping
also the first program that loads after the will take place
bootloader. › Examples: Unix, Linux, Multics and
Bootloader is a program that loads and starts the Windows
boot time tasks and processes of an OS. It also 3. Distributed operating system
places the OS of a computer into memory. › Distributed systems use multiple central
processors to serve multiple real-time
TYPES OF OPERATING SYSTEM applications and multiple users. Data
Operating systems are there from the very first processing jobs are distributed among
computer generation and they keep evolving with the processors accordingly.
time. › The processors communicate with one
another through various communication
Types of operating systems which are most lines (such as high-speed buses or
commonly used: telephone lines). These are referred as
1. Batch operating system loosely coupled systems or distributed
› The user of a BOS never directly interacts systems. Processors in a distributed
with the computer. system may vary in size and function.
› Every user prepares his or her job on an These processors are referred as sites,
offline device like a punch card and nodes, computers, and so on.
submit it to the computer operator. › Examples: Telecom Network, WWW,
› To speed up processing, jobs with similar Cloud Computing, etc.
needs are batched together and run as a 4. Network operating system
group. › A NOS runs on a server and provides the
› The programmers leave their programs server the capability to manage data,
with the operator then operator sorts the users, groups, security, applications, and
programs with similar requirements into other networking functions.
batches. › The primary purpose of the network
2. Time-sharing operating systems operating system is to allow shared file
› Time-sharing or multitasking is logical and printer access among multiple
extension in which CPU switches jobs so computers in a network, typically a local
frequently that users can interact with area network (LAN), a private network or
each job while it is running, creating to other networks.
interactive computing. › Examples: Microsoft Windows Server
› Multiple jobs are executed by the CPU by 2003, Microsoft Windows Server 2008,
switching between them, but the switches UNIX, Linux, Mac OS X Server, Novell
Applied Operating System
MODULE 1 – IT0035
NetWare, and BSD/OS (Berkeley Software • Each device controller has a local buffer.
Design). • CPU moves data from/to main memory
5. Real-time operating system to/from local buffers.
› RTOS is an operating system intended to • I/O is from the device to local buffer of
serve real-time systems/applications that controller.
process data as it comes in, mostly • Device controller informs CPU that it has
without buffer delay. finished its operation by causing an interrupt.
› The time interval required to process and
respond to inputs is very small. This time What is an Interrupt?
interval is called response time. o Interrupt is a signal emitted by hardware or
› Real-time systems are used when there software when a process or an event needs
are time requirements are very strict like immediate attention.
missile systems, air traffic control systems, o It alerts the processor temporarily to a high
robots, etc. priority process requiring interruption of the
› Examples: LynxOS, OSE, QNX, RTLinux, current working process and then return to its
VxWorks, Windows CE previous task.
6. Handheld operating system o Types of Interrupts:
› It is also known as Mobile OS which is ▪ Hardware interrupt
built exclusively for a mobile device, such ▪ Software interrupt
as a smartphone, personal digital o An operating system is interrupt driven.
assistant (PDA), tablet, wearable devices
Hardware Interrupt
or other embedded mobile OS.
› Examples: Android, Symbian, iOS, • a signal created and sent to the CPU that is
BlackBerry OS and Windows Mobile. caused by some action taken by a hardware
device.
COMPUTER SYSTEM ORGANIZATION • Example: When a key is pressed or when the
mouse is moved.
Software Interrupt
• arises due to illegal and erroneous use of an
instruction or data. It often occurs when an
application software terminates or when it
requests the operating system for some
• One or more CPUs, device controllers connect service.
through common bus providing access to • Example: stack overflow, division by zero,
shared memory. invalid opcode, etc. These are also called
• Concurrent execution of CPUs and devices traps.
completing for memory cycles.
• I/O devices and the CPU can execute Interrupt Handling
concurrently. × The operating system preserves the state of
• Each device controller is in charge of a the CPU by storing registers and the program
particular device type. counter.
Applied Operating System
MODULE 1 – IT0035
× Determines which type of interrupt has COMPUTER SYSTEM ARCHITECTURE
occurred: × Most systems use a single general-purpose
o Polling – operating system sends signal processor (PDAs through mainframes)
to each devices asking if they have a × Most systems have special-purpose
request processors as well
o Vectored interrupt system – × Multiprocessors systems growing in use and
requesting device sends interrupt to the importance
operating system. • Also known as parallel systems or
× Separate segments of code determine what tightly-coupled systems
action should be taken for each type of • Advantages include
interrupt › Increased throughput
› Economy of scale
OPERATING SYSTEM OPERATORS
› Increased reliability – graceful
› Dual-mode operation allows OS to protect degradation or fault tolerance
itself and other system components • Two types
› User mode and kernel mode › Asymmetric Multiprocessing
› Mode bit provided by hardware › Symmetric Multiprocessing
o Provides ability to distinguish when
system is running user code (1) or kernel MULTIPROCESSOR SYSTEMS
code (0)
Advantages:
o Some instructions designated as
1. Increased throughput. Increasing the
privileged, only executable in kernel
number of processor, expect to get more
mode
work done in less time.
o System call changes mode to kernel,
2. Economy of scale. It can cost less than
return from call resets it to user
equivalent multiple single-processor
o A system call is a way for programs to
systems because they can share peripherals,
interact with the OS. A computer
mass storage and power supplies.
program makes a system call when it
3. Increased reliability. Functions can be
makes a request to the OS‘s kernel.
distributed properly among several
PROCESSOR SYSTEM processors. If one processor fails, the other
processor can pick-up the task.
Single-Processor System
› There is one main CPU capable of executing The multiprocessor systems in use today are of
a general-purpose instruction set, including two types
instructions from user processes. 1. Asymmetric multiprocessing. Each
Multiprocessor System processor is assigned a specific task. A boss
› Also known as parallel-system or processor controls the system and the other
multicore. processors either look to the boss for
› First appeared in servers and now in instructions or have predefined tasks. Boss-
smartphones and tablet computers. worker relationship.
Applied Operating System
MODULE 1 – IT0035
2. Symmetric multiprocessing (SMP). The ▪ Now portals allowing networked
most commonly used. In which each and remote systems access to
processor performs all tasks within the same resources
operating system. All processors are peers o Home networks
and no boss-worker relationship. ▪ Used to be single system, then
The difference between symmetric and modems
asymmetric may result from either hardware or ▪ Now firewalled, networked
software. o Mobile computing
▪ Refers to computing on handheld
× A recent trend in CPU design is to include
smartphones and tablet
multiple computing cores on a single chip.
computers.
Such multiprocessor systems are termed
o Distributed system
multicore. They can be more efficient than
▪ It is a collection of physically
multiple chips with single core.
separate, possibly heterogeneous
× A dual-core design with two cores on the computer systems that are
same chip. Each core has its own register set networked to provide users with
as well as its own local cache. access to the various resources that
CLUSTERED SYSTEMS the system maintains.
▪ Network operating system is an
• Like multiprocessor systems, but multiple
operating system that provides
systems working together.
services across the network.
• Usually sharing storage via a storage-area
o Client-Server Computing
network (SAN)
▪ Dumb terminals succeeded by smart
• Provides a high-availability service which
PCs
survives failures
▪ Many systems now servers,
o Asymmetric clustering has one
responding to requests generated
machine in hot-standby mode
by clients
o Symmetric clustering has multiple
• Compute-server provides an
nodes running applications,
interface to client to request
monitoring each other
services (i.e. database)
• Some clusters are for high-performance
• File-server provides interface
computing (HPC)
for clients to store and retrieve
COMPUTING ENVIRONMENT files
• Another model of distributed system
• Traditional computer - blurring over time
• P2P does not distinguish clients and servers
o Office environment
o Instead all nodes are considered peers
▪ PCs connected to a network,
o May each act as client, server or both
terminals attached to mainframe or
o Node must join P2P network
minicomputers providing batch
▪ Registers its service with central
and timesharing
lookup service on network, or
Applied Operating System
MODULE 1 – IT0035
▪ Broadcast request for service and • Cloud Computing Service Models
respond to requests for service via o Software as a service (SaaS) – one or
discovery protocol more applications available via the
o Examples: Napster and BitTorrent Internet
• Virtualization o Platform as a service (PaaS) – software
o It is a technology that allows operating stack ready for application use via the
systems to run as applications within Internet
other operating system. o Infrastructure as a service (IaaS) –
o It is one member of the class software servers or storage available over the
that also includes emulation. Emulation Internet
is used when the source CPU type is
different from the target CPU type.
o Example: virtual machine,
OracleVirtualBox
• Cloud Computing
o It is a type of computing that delivers
computing, storage and even
applications as a service across a
network.
o It is a logical extension of virtualization
▪ Public cloud – cloud available via
the Internet OPEN-SOURCE OPERATING SYSTEM
▪ Private cloud – cloud run by a › Open Source operating systems are
company for that company’s own released under a license where the copyright
use holder allows others to study, change as well
▪ Hybrid cloud – cloud that includes as distribute the software to other people.
both public and private › Counter to the copy protection and Digital
Rights Management (DRM) movement
› Started by Free Software Foundation (FSF),
which has “copyleft” GNU Public License
(GPL)
› Examples: GNU(GNU’s Not Unix)/Linux, BSD
UNIX (including core of Mac OS X), and Sun
Solaris
