Transcript operating system

Introduction to Computing
Lecture # 5
Outline
• System software and its components
• Operating system and its functions
• Device drivers and utility programs
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System Software
• System software enables the applications software to
interact with the computer and helps the computer
manage its internal and external resources. (Williams &
Sawyer)
• System software is a collection of computer programs
that manage the resources of a computer and
facilitate access to those resources. (Schneider & Gersting)
• There are three basic components of system
software:
1. Operating systems
2. Device drivers
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3. Utility programs
The Components of System Software
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1.
Operating system the principal
component of
system software
2.
Device drivers help the computer
control peripheral
devices
3.
Utility programs support, enhance,
or expand existing
programs
The Operating System: What It Does
• The operating system consists of the master system
of programs that manage the basic operations of the
computer.
• These programs provide resource management
services of many kinds.
• They handle the control of and use of hardware
resources:
–
–
–
–
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Disk space
Memory
CPU
Peripheral devices
The Operating System: What It Does
• Booting - the process of loading an operating system
into a computer’s main memory
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The Operating System: What It Does
• Booting
– diagnostic routines first start up and test the main
memory, the central processing unit, and other
parts of the system to make sure they are running
properly.
– BIOS (basic input/output system) will be copied to
main memory to help the computer interpret
keyboard characters or transmit characters to the
display screen or to a diskette.
– Then the boot program obtains the operating
system, usually from hard disk, and loads it into the
computer’s main memory.
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The Operating System: What It Does
• OS provides user interface: user-controllable display
screen that allows you to interact with your computer
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The Operating System: What It Does
CPU Management
• Supervisor (kernel) – manages the CPU. It
remains in main memory while the computer
is running, and directs other “non-resident”
programs to perform tasks that support
application programs.
• Example
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– Writing a report using a word processor program
and want to print out a portion of it while continuing
to write.
– OS will select a printer
– Executing printer driver
The Operating System: What It Does
Memory Management
• The OS manages memory via:
– Partitioning - division of memory into separate
areas called partitions, each of which can hold a
program or data.
– Foreground/background - division of memory into
higher priority (foreground) and lower priority
(background) areas.
– Queues - temporary line-ups for programs waiting
to be executed. Programs that are to be executed
wait on disk in queues.
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The Operating System: What It Does
File Management
• A file is a named collection of related
information.
• A file can be a program or it can be a data file.
• Files are stored on hard disks and other
secondary storage devices.
• OS records the storage location of all files.
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The Operating System: What It Does
Task Management
• A task is an operation such as storing, printing or
calculating.
• A computer is required to perform many different
tasks at once.
• Some operating systems also handle more than one
program at the same time.
• Among the ways operating systems manage tasks in
order to run more efficiently are:
– Multitasking
– Multiprogramming
– Time sharing
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– Multiprocessing
The Operating System: What It Does
Task Management
• Multitasking
– Multitasking is the execution of two or more programs by one
user concurrently on the same computer with one CPU.
– Executing more than one program concurrently.
– Earlier OS could do only single-tasking
– Today, multitasking Operating Systems are used.
– OS directs the processor to spend a predetermined amount
of time executing the instructions for each program, one at a
time.
– A small part of each program is executed, and the cycle
keeps on repeating until processing is complete.
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The Operating System: What It Does
Task Management
• Multiprogramming
– Multiprogramming is the execution of different
users’ programs concurrently on a multi-user
operating system.
– Concurrent execution of different users’ programs
– The processor spends a certain amount of time
executing each user’s program.
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The Operating System: What It Does
Task Management
• Time sharing
– In time-sharing, a single computer processes the
tasks of several users at different stations in roundrobin fashion.
– Round-robin processing of programs for several
users.
– Time slicing is used for time sharing.
– A time slice is a fraction of a second.
– The computer may rapidly switch back and forth
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among different tasks.
Introduction to Computing
Lecture # 5
The Operating System: What It Does
Task Management
Multitasking Vs Time-sharing
• Multitasking
• Time-sharing
• The processor directs the
programs to take turns
accomplishing small tasks
or events, such as, a
calculation, search a
record, print a part.
• The computer spends a
fixed amount of time with
each program before
going on to the next one.
• Each task may take a
different amount of time.
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The Operating System: What It Does
Task Management
• Multiprocessing
– Multiprocessing is processing done by two or more
computers or processors linked together to perform
work simultaneously.
– Simultaneous processing of two or more programs
by multiple computers
– Processing instructions from different programs or
different instructions within the same program at
once.
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The Operating System: What It Does
Task Management
• Two possible approaches to multiprocessing:
– Coprocessing - the controlling CPU works
together with specialized microprocessors called
coprocessors, each of which handles a particular
task.
– Parallel processing - several full-fledged
processors work together on the same tasks,
sharing memory.
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The Operating System: What It Does
Task Management
Number of
Users
Number of
Processors
Order of
Processing
Multi-tasking
One
One
Concurrently
Multiprogramming
Multiple
One
Concurrently
Time sharing
Multiple
One
Round robin
Multiprocessing
One or more
Two or more
Simultaneously
Processing of two or more programs
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The Operating System: What It Does
• Formatting (initializing) a disk - the process of
preparing that disk so that it can store data or
programs
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Other System Software:
Device Drivers & Utility Programs
• Device drivers -
specialized software
programs that allow
input and output
devices to
communicate with the
rest of the computer
system
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Other System Software:
Device Drivers & Utility Programs
• Many basic device derivers come with system
software.
• If, however, we buy a new peripheral device,
such as a mouse, scanner, or printer, the
package will include a device driver (probably
on a CD-ROM).
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Utilities: Service Programs
• Utility Programs, also known as service programs,
perform tasks related to the control and allocation of
computer resources.
• They enhance existing functions or provide services
not supplied by other system software programs.
• Built-in utilities – as part of the operating system.
• External utility programs – such as Norton Desktop
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Utilities: Service Programs
• Backup utility
– Program which makes a duplicate copy of the
information onto hard disk or removable media.
– Example: Norton Backup
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Utilities: Service Programs
• Data-recovery utility
– Program which restores data that has been
physically damaged or corrupted.
– Data can be damaged by viruses, bad software,
hardware failure, and power fluctuations that occur
while data is being written/recorded.
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Utilities: Service Programs
• Virus
– A virus consists of hidden programming
instructions that are buried within an application or
system program.
– They copy themselves to other programs, causing
destruction.
– Viruses are spread when people exchange floppy
disks or download information from computer
networks or the Internet
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Utilities: Service Programs
• Antivirus software
– Program that scans hard disks, floppy disks, and
memory to detect viruses.
– Some utilities destroy the virus as soon as it is
detected and others notify the user of possible viral
behavior.
– Examples of antivirus software are Norton
AntiVirus, Dr. Solomon’s Anti-Virus Toolkit, McAfee
VirusScan, and Webscan.
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Utilities: Service Programs
• Data compression utility
– In order to gain more disk space, the user has four
options:
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•
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delete old files
buy a new hard disk with more capacity
add an hard drive
or buy a data compression utility.
– Program which removes redundant elements,
gaps, and unnecessary data from a computer’s
storage space so that less space (fewer bits) is
required to store or transmit data.
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Utilities: Service Programs
• Fragmentation - the
scattering of portions of
files about the disk in
nonadjacent areas, thus
greatly slowing access
to the files
• Defragmenter utility program that finds all the
scattered files on your
hard disk and
reorganizes them as
contiguous files
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Utilities: Service Programs
• Disk scanner and disk
cleanup utilities:
• Detect & remove
unnecessary files
• Detect & correct disk
problems
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