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Operating System Fundamentals
Dr. Ashraf Said
Math. & Comp. Sc. Dept.Faculty of Science
Alexandria University
Lecture 1 : Introduction and Concepts
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Outline
What is an Operating System? Types of Computer Systems Simple Batch Systems
Multi-programmed Batched Systems
Time-Sharing Systems
Personal-Computer Systems
Parallel Systems
Distributed Systems Real-Time Systems
Handheld Systems
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What is an Operating System?
A software that controls the hardware.
Processors, storage, input/output devices,
communication devices and data.
A software that manages the hardware.
A software that acts as a resources allocator.
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How Can We Define Operating
System?Operating System (OS) is a program that
controls the execution of application
programs. It is also defined as being themean through which controlling of allocation
and usage of hardware resources and
coordinating of all software activities within acomputer is done.
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Where Can an OS Fit?
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Operating System Objectives
Convenience: Makes the computer more convenient to use.
Ease of Communication: Between Computer and user through a friendly
user interface. Among system components.
Abstraction: Hardware-independent programming model.
Efficiency: Allows computer system resources to be used in
an efficient manner.
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Operating System Objectives (contd)
Monitoring and Alerting: Monitors and alerts failures and problems.
Ability to Evolve:
Permit effective development, testing, and introduction of
new system functions without interfering with the services.
Protection:
A layer of security is to be added to ensure that a certain
level of security is maintained to protect users data.
Increasing performance: Maximizing the throughput and Minimizing time needed to
execute command.
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Services Provided by the Operating
System Program development: Such as editors and
debuggers.
Program execution:
Load program and data, initialize environment. Access to I/O devices:
Attempt to read from and write to the ports and units.
Controlled access to data: Access protection.
System access: User authentication.
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Services Provided by the Operating
System (contd) Error detection and response:
In case of error occurring, an error message
should be displayed.
Internal and external hardware errors: Memory error.
Device failure.
Software errors: Arithmetic overflow.
Access forbidden memory locations.
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Services Provided by the Operating
System (contd) Accounting:
Collect statistics.
Monitor performance.
Is used to anticipate future enhancements?
Is usedfor billing users?
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Functions of an Operating System on a
Network
1. Sharing H/W among users.
2. Allowing users to share data.
3. Preventing users from interfering with oneanother.
4. Scheduling resources among users.
5. Organizing data forsecure and rapidaccess.
6. Handling network communications.
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Components of Computer System Input devices
Processing devices (Central Processing Unit) Output devices
Storage devices
Applications software
Word Processing Spreadsheet - Database
System software
Operating System - Utilities Users, orend users, are the people in the computing environment
who need the output that computer systems produce. Programmers are the people whose job it is to write programs to
supply this information.
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Layers of Computer System
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Computer-System Operation I/O devices and the CPU can
execute concurrently.
Each device controlleris
responsible of a particular
device type.
Each device controller has alocal buffer(memory).
CPU moves data from/to main memory to/from local buffers
I/O is from the device to local buffer of controller.
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Storage-Device Hierarchy
Storage systems organized in
hierarchy.
Speed
Cost
Volatility
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What is a Kernel?
Module Kernel is responsiblefor:
Memory allocation.
Garbage collection Object finalization
Module termination
Interfacing to theunderlying operating
system, and clock functions
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Types of Computer Systems
Simple Batch Systems
Multi-programmed Batched Systems
Time-Sharing Systems
Personal-Computer Systems Parallel Systems
Distributed Systems
Real-Time Systems Handheld systems
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Simple Batch System
Runs only one job at a time.
Smoothed transition between jobs to getmaximum utilization.
Programs/data submitted in groups or
batches.
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Multi-programmed Batch System
Usesjob scheduling to increase resources
utilization.
Stores more than one program in memory.
Based on the fact that any one job rarely
utilizes all computer resources.
When one job is waiting for an I/O, other can
use CPU and/or any other I/O.
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Time Sharing System
Uses time sharing to switch between multiple
jobs.
Interactive. Provides a low response time to
users.
Developed to large numbers of simultaneously
interactive users.
A program shares in time only if it exists inmemory.
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Personal System (Desktop)
Every user has his own memory, processors,
and I/O devices.
Became possible after investing micro-
processors.
Computing may be distributed to the sites
rather than central place.
Data may be shared among users throughnetworks.
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Distributed System
Computers that communicate using a network:WAN (Wide area network) orLAN (Local area
network), i.e. independent computers that works
as a single system.
Client-Server:A client is a computer that needsservice.A serveris a S/W or a H/W that do a
single service (Printing, graphics, DB, e-mail).
Peer-To-Peer: Decentralized computers provide
services to peers.
Incremental growth.
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Parallel System
A computer contains two or more CPUs that
share a common bus.
A job Should be split to discrete (independent)
small jobs.
Exponential speed up in computation needs
exponential increase in the number of
processors.
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Real-time System
Often used as a control device in a dedicated
application such as: a. Controlling scientific
experiments, b. Medical imaging systems, c.
Industrial control systems. Well-defined fixed-time constraints.
Real-time system may be eitherhard orsoft
system
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Real-time System (contd)
Hard real-time system: Secondary storage limited or absent
Data stored in short term memory.
Conflicts with time-sharing systems.
Not supported by general purpose OS.
Soft real-time system:
Useful in applications (multimedia, virtual reality).
RequireAdvanced OS features.
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Handheld Systems
Personal Digital Assistants (PDAs)
Cellular telephones
Issues:
Limited memory
Slow processors
Small display screens
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Computer Categories
Computers are generally classified in one of fourcategories: small, or microcomputers; medium-sized, ormidrange computers; large, ormainframecomputers; and super-large, or supercomputers.An emerging new category is mobile devices, as
discussed next.
In general, the larger the computer, the greater itsprocessing power. For example, big computers can
process data at faster speeds and can perform morecomplicated types of processing than can smallcomputers. Big computers can also accommodatelarger, more powerful support devices. **
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Computer Categories
Mobile devices
Microcomputers
Midrange computers
Mainframe computers
Supercomputers
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Mobile DevicesA mobile device is loosely defined as a very small
computing device based on a wireless phone orpager.
Such devices usually offerlimited Internet access in
addition to theirregular functions, such as placingphone calls and sending and receiving pages or
messages.
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Personal Computers
A technological breakthrough in the early 1970s
made it possible to produce an entire CPU on asingle silicon chip smaller than a dime. These
computers-on-a-chip, or microprocessors, can be
mass-produced at a very low cost.
Microprocessors also made it possible to build
inexpensive computer systems small enough to fit on
a desk or your lap.
The small computers at the heart of these systems
have come to be called microcomputers or
personal computers (PCs).
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Personal Computers, contd. Although most microcomputers designed for home or
business use are desktop computers, smaller PCs areavailable. Portable PCs include notebook, tablet,handheld, and pocketcomputers.
PCs designed for network use only are referred to as
network computers orthin clients.PCs or devicesdesigned for Internet access only are called Internetappliances.
Most PC users choose between two major computerplatformswhen they buy a computerPC compatiblesand Macintosh computers. Often, people refer to PC-compatible computers as the Windows platform or as IBM-compatible PCs.
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Personal Computers, contd.
PC compatiblea personal computer based
on Intel microcomputer or compatible CPUs
Macintosha type of personal computer
manufactured by Apple
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Midrange ComputersMidrange computers (orminicomputers) are regarded as
medium-sized computers. Most of them fall betweenmicrocomputers and mainframes in their processingpower.
A small or medium-sizedcompany, for example, may
find a microcomputer system
just too small or too slow to
handle its currentvolume of work.
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Mainframes Mainstay of almost all large organizations
Specialize in high-volume processing of business transactions
Mainframes often operate24 hours a day, serving dozens
of users on terminals
during regular business
hours and processing big jobssuch as payroll and billing late
at night.
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SupercomputersSome organizations, such as large scientific research
laboratories, have extraordinary demands for processingpower.
To meet applications needs such as very fast speeds andextreme degrees of accuracy, a few vendors offer verypowerful computers, called supercomputers.
Many supercomputers today
are created by linking together
multiple PCs or microprocessor
chips.
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Computer Categories vs. Systems
Mobile devices: Handheld systems.
Microcomputers: Desktop systems.
Midrange computers: Desktop & Real-timesystems.
Mainframe computers: Batch & Time-share (Hybrid
systems).
Supercomputers: Parallel & distributed systems.
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Useful Website
www.osdata.com