System is a collection of programs which control the overall functions of which control the overall functions of computer.
An operating system is a program that acts as an interface between the user of a computer and the computer hardware. The purpose of operating system is to provide an environment in which a user can execute programs in a efficient manner. Operating system also acts as a platform on which various application programs such as word processor and excel are executed.
System is a collection of programs which control the overall functions of which control the overall functions of computer.
An operating system is a program that acts as an interface between the user of a computer and the computer hardware. The purpose of operating system is to provide an environment in which a user can execute programs in a efficient manner. Operating system also acts as a platform on which various application programs such as word processor and excel are executed.
An operating system (OS) is a collection of software that manages computer hardware resources and provides common services for computer programs. The operating system is an essential component of the system software in a computer system. Application programs usually require an operating system to function.
Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.
For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware,[1][2] although the application code is usually executed directly by the hardware and will frequently make a system call to an OS function or be interrupted by it. Operating systems can be found on almost any device that contains a computer—from cellular phones and video game consoles to supercomputers and web servers.
Examples of popular modern operating systems include Android, BSD, iOS, Linux, OS X, QNX, Microsoft Windows,[3] Windows Phone, and IBM z/OS. All these, except Windows, Windows Phone and z/OS, share roots in UNIX.
Presentation Regarding functions of operating systems and their working and other information regarding their uses and types. Useful for Students and other for knowing better about them.
Pleases Send Your Valuable Comments regarding it
In the given presentation, process overview,process management scheduling typesand some more basic concepts were explained.
Kindly refere the presentation.
Operating System is a collection of programs that handle many of technical details Related to using a computer. In many ways ,an operating system is most important type of computer program. Without it your computer would be useless.
Definition:-Operating system are program that manages resources, provide user interface, and run applications.
Functions Of Operating System
Features Of Operating Systems
Advantages of Linux
Operating System - Types Of Operating System Unit-1abhinav baba
In This Slide There is Operating System And it's types ( Types of operating system)
Batch Operating System
Network Operating System
Time Sharing Operating System
Real Time Operating System
Distributed Operating System
An operating system (OS) is a collection of software that manages computer hardware resources and provides common services for computer programs. The operating system is an essential component of the system software in a computer system. Application programs usually require an operating system to function.
Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.
For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware,[1][2] although the application code is usually executed directly by the hardware and will frequently make a system call to an OS function or be interrupted by it. Operating systems can be found on almost any device that contains a computer—from cellular phones and video game consoles to supercomputers and web servers.
Examples of popular modern operating systems include Android, BSD, iOS, Linux, OS X, QNX, Microsoft Windows,[3] Windows Phone, and IBM z/OS. All these, except Windows, Windows Phone and z/OS, share roots in UNIX.
Presentation Regarding functions of operating systems and their working and other information regarding their uses and types. Useful for Students and other for knowing better about them.
Pleases Send Your Valuable Comments regarding it
In the given presentation, process overview,process management scheduling typesand some more basic concepts were explained.
Kindly refere the presentation.
Operating System is a collection of programs that handle many of technical details Related to using a computer. In many ways ,an operating system is most important type of computer program. Without it your computer would be useless.
Definition:-Operating system are program that manages resources, provide user interface, and run applications.
Functions Of Operating System
Features Of Operating Systems
Advantages of Linux
Operating System - Types Of Operating System Unit-1abhinav baba
In This Slide There is Operating System And it's types ( Types of operating system)
Batch Operating System
Network Operating System
Time Sharing Operating System
Real Time Operating System
Distributed Operating System
UNIT I OPERATING SYSTEM OVERVIEW
Computer System Overview-Basic Elements, Instruction Execution, Interrupts, Memory Hierarchy, Cache Memory, Direct Memory Access, Multiprocessor and Multicore Organization. Operating system overview-objectives and functions, Evolution of Operating System.- Computer System Organization Operating System Structure and Operations- System Calls, System Programs, OS Generation and System Boot.
operating systems concepts, ch-01, third level, Faculity of Applied Scinces, Seiyun University. انظمة التشغيل لطلاب المستوى الثالث بكلية العلوم التطبيقية المحاضرة 01
Topic covers:
what is operating system?
need of operating system
Loading of operating system
types of operating system?
Functions of operating system?
System Security Plan?
Hardening of operating system
This ppt discusses about Switch Security Configuration including Port Security configuration, Mitigating DHCP attacks, APR attacks, STP attacks and usage of DHCP Snooping and Portfast & BPDUGuard.
This ppt describes about Module-12 of SRWE course and covers the concepts related to Introduction to Wireless, Components of WLANs, WLAN Operation, CAPWAP Operation, Channel Management, WLAN Threats and Securing WLANs.
This ppt includes contents related to Remote Site WLAN Configuration, Configure a Basic WLAN on the WLC, Configure a WPA2 Enterprise WLAN on the WLC & Troubleshoot WLAN Issues
This ppt discusses the concepts related to Static IP routing, types of static routes, configuration of IP Static Routes, IP Default Static Routes, Floating Static Routes & Static Host Routes
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Protecting Your Data and Privacy- Cisco: Intro to Cybersecurity chap-3Mukesh Chinta
This ppt focuses on your personal devices and your personal data. It includes tips for protecting your devices, creating strong passwords and safely using wireless networks. It also discusses maintaining your data securely.
Attacks, Concepts and Techniques - Cisco: Intro to Cybersecurity Chap-2Mukesh Chinta
This ppt covers the ways that cybersecurity professionals analyze what has happened after a cyberattack. It explains security software and hardware vulnerabilities and the different categories of security vulnerabilities.
It consists of CPU scheduling algorithms, examples, scheduling problems, realtime scheduling algorithms and issues. Multiprocessing and multicore scheduling.
Gives an overview about Process, PCB, Process States, Process Operations, Scheduling, Schedulers, Interprocess communication, shared memory and message passing systems
This is the eighth Chapter of Cisco Cyber Security Essentials course Which discusses the safeguarding the cyber security domains and steps to become a cyber security professional.
This is the Fourth Chapter of Cisco Cyber Security Essentials course Which discusses the implementation aspects of Confidentiality via Encryption, Access Control Techniques
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
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About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
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Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
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Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
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Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
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2. What is an Operating System??
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.
An Operating System (shortly OS) is a set of programs that
manage computer hardware resources and provide
common services for application software.
Based on the need and usage, some operating systems are
designed to be , others to be , and
others to be some combination of the two.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
3. Computer System Structure
Computer system can be divided into four components:
• CPU, memory, I/O devices
• Controls and coordinates use of hardware among various
applications and users
– define the ways in which the
system resources are used to solve the computing
problems of the users
• Word processors, compilers, web browsers, database systems,
video games
• People, machines, other computers
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
4. The dominant desktop operating system is Microsoft Windows
with a market share of around 82.74%. macOS by Apple Inc. is
in second place (13.23%), and the varieties of Linux are
collectively in third place (1.57%).
5. What Operating Systems Do??
In case of a single user system, the operating system is designed mostly for ease
of use, with some attention paid to performance and none paid to resource
utilization—how various hardware and software resources are shared.
In cases, where a user sits at a terminal connected to a mainframe or a
minicomputer, the OS is designed to maximize resource utilization— to assure
that all available CPU time, memory, and I/O are used efficiently and that no
individual user takes more than her fair share.
In some cases, users of workstations have dedicated resources, but frequently
use shared resources from servers. their operating system is designed to
compromise between individual usability and resource utilization.
Handheld computers are resource poor, and are optimized for usability and
battery life.
Some computers have little or no user interface, such as embedded computers in
devices and automobiles. The OS are designed to run without human
intervention.
6. What Operating Systems Do??
• 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
7. Definition of OS
• 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
• 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.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
8. Computer System Organization
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. Each device
controller is in charge of a specific type of device.
The CPU and the device controllers can execute in parallel,
competing for memory cycles. To ensure orderly access to the shared
memory, a memory controller synchronizes access to the memory.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
9. Computer System Operation
For a computer to start running, when it is powered up or rebooted—it needs to
have an initial program to run called a .
It is stored within the computer hardware in or
known by
the general term firmware.
It initializes all aspects of the system, from CPU registers to device controllers
to memory contents.
To start execution of the OS, the bootstrap program must locate the Operating-
system kernel and load into memory.
Once the kernel is loaded and executing, it can start providing services to the
system and its users. Some services are provided outside of the kernel, by
system programs that are loaded into memory at boot time to become system
processes, or system daemons that run the entire time the kernel is running.
Once this phase is complete, the system is fully booted, and the system waits
for some event to occur.
Operating Sytems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
10. The occurrence of an event is usually signaled by an 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
(also called a ).
When the CPU is interrupted, it stops what it is doing and immediately
transfers execution to a fixed location. The fixed location usually contains the
starting address where the service routine for the interrupt is located. The
interrupt service routine executes; on completion, the CPU resumes the
interrupted computation.
11. Storage Structure
The CPU can load instructions only from memory, so any programs
to run must be stored there.
General-purpose computers run most of their programs from
rewritable memory, called (also called
or RAM). Main memory commonly is implemented in a
semiconductor technology called
.
Because ROM cannot be changed, only static programs, such as the
bootstrap program, are stored there.
EEPROM can be changed but cannot be changed frequently and so
contains mostly static programs.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
12. All forms of memory provide an array of bytes. Each byte has its own address.
Interaction is achieved through a sequence of load or store instructions to
specific memory addresses.
The operands for all arithmetic and logic operations are contained in registers.
To operate on data in main memory, the data is first copied into registers. A
load operation copies data from main memory into a register. A store operation
copies data from a register into main memory.
A typical instruction–execution cycle, as
executed on a system with a von Neumann
architecture, first fetches an instruction from
memory and stores that instruction in the
instruction register. The instruction is then
decoded and may cause operands to be
fetched from memory and stored in some
internal register. After the instruction on the
operands has been executed, the result may be
stored back in memory.
13. Though its preferred to have all the programs and data to reside in the main
memory, the following constraints are present:
1. Main memory is usually too small to store all needed programs and data
permanently.
2. Main memory is a volatile storage device that loses its contents when power is
turned off or otherwise lost.
Thus, most computer systems provide secondary storage as an extension of
main memory. The main requirement for secondary storage is that it be able to
hold large quantities of data permanently.
The most common secondary-storage device is a magnetic disk, which
provides storage for both programs and data.
Others include cache memory, CD-ROM, magnetic tapes, and so on. Each
storage system provides the basic functions of storing a datum and holding that
datum until it is retrieved at a later time. The main differences among the
various storage systems lie in speed, cost, size, and volatility.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
17. I/O Structure
Management of I/O devices is a very important part of the operating system.
The range of devices on a modern computer is hugely varied, from mice,
keyboards, disk drives, display adapters, USB devices, network connections,
audio I/O, printers, special devices for the handicapped etc.
Device drivers are software modules that can be plugged into an OS to handle a
particular device. The Device Controller works like an interface between a
device and a device driver.
Device controller is an intermediary between Device and OS and the Device
driver is an interface between device controller and OS. Device drivers are
modules that can be plugged into an OS to handle a particular device or
category of similar devices.
There is always a device controller and a device driver for each device to
communicate with the Operating Systems. A device controller may be able to
handle multiple devices.
Seven or more devices can be attached to the small computer-systems interface (SCSI)
controller
Operating Sytems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
18.
19. Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
The controller starts the transfer of
data from the device to its local
buffer.
Once the transfer of data is complete,
the device controller informs the
device driver via an interrupt that it
has finished its operation.
The device driver then returns control
to the operating system, possibly
returning the data or a pointer to the
data if the operation was a read.
22. Computer-System Architecture
In computer engineering, computer architecture is a set of rules and
methods that describe the functionality, organization, and
implementation of computer systems.
A computer system can be organized in a number of different ways,
which can be categorized roughly according to the number of
general-purpose processors used.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
23. Till recently, most systems use single processor systems. They
perform only one process at a given time, and it carries out the next
process in the queue only after the current process is completed.
Almost all single processor systems have other special-purpose
processors which may come in the form of device-specific
processors, such as disk, keyboard, and graphics controllers; or, on
mainframes, they may come in the form of more general-purpose
processors, such as I/O processors that move data rapidly among the
components of the system.
These processors execute only a limited system programs and do not run the
user program.
A single processor system is defined as “ A system that has only one
general purpose CPU, is considered as single processor system.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
24. Some systems that have two or more processors are also known as parallel
systems or tightly coupled systems.
Mostly the processors of these systems share the common system bus,
memory and peripheral (input/output) devices. These systems are fast in
data processing and have capability to execute more than one program
simultaneously on different processors.
This type of processing is known as multiprogramming or multiprocessing.
Multiple processors further divided in two types.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
25. Multiprocessing operating system or the parallel system support the use of
more than one processor in close communication. The advantages of the
multiprocessing system are:
• Increased Throughput − By increasing the number of processors, more work can
be completed in a unit time.
• Cost Saving − Parallel system shares the memory, buses, peripherals etc.
Multiprocessor system thus saves money as compared to multiple single systems.
Also, if a number of programs are to operate on the same data, it is cheaper to
store that data on one single disk and shared by all processors instead of using
many copies of the same data.
• Increased Reliability − In this system, as the workload is distributed among
several processors which results in increased reliability. If one processor fails
then its failure may slightly slow down the speed of the system but system will
work smoothly.
28. ꙮ Multiprocessing adds CPUs to increase computing power. If
the CPU has an integrated memory controller, then adding
CPUs can also increase the amount of memory addressable in
the system.
ꙮ Multiprocessing can cause a system to change its memory access
model from uniform memory access (UMA) to non-uniform memory
access (NUMA).
ꙮ A recent trend in CPU design is to include multiple computing
cores on a single chip. Such multiprocessor systems are
termed multicore.
They can be more efficient than multiple chips with single cores
because on-chip communication is faster than between-chip
communication.
In addition, one chip with multiple cores uses significantly less
power than multiple single-core chips.
29. ꙮ While multicore systems are multiprocessor systems, not all
multiprocessor systems are multicore.
30. Another type of multiprocessor system is a ,
which gathers together multiple CPUs. These systems are considered
loosely coupled.
Clustered systems differ from the multiprocessor systems in that they
are composed of two or more individual systems—or nodes—joined
together. Each node may be a single processor system or a multicore
system.
The definition of the term clustered is not concrete; the general
accepted definition is that clustered computers share storage and are
closely linked via LAN networking.
Clustering is usually used to provide —that
is, service will continue even if one or more systems in the cluster
fail.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
31. A layer of cluster software runs on the cluster nodes. Each node can
monitor one or more of the others. If the monitored machine fails, the
monitoring machine can take ownership of its storage, and restart the
application(s) that were running on the failed machine. The failed
machine can remain down, but the users and clients of the application
would only see a brief interruption of service.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
32. Clustering can be structured asymmetrically or symmetrically.
- In this, one machine is in hot-standby mode while
the other is running the applications. The hot-standby host (machine) does
nothing but monitor the active server. If that server fails, the hot standby
host becomes the active server.
- In this, two or more hosts are running applications,
and they are monitoring each other. This mode is obviously more efficient,
as it uses all of the available hardware.
Since a cluster consists of several computer systems connected via a network,
clusters can also be used to provide high-performance computing environments.
Such systems can supply significantly greater computational power than single-
processor/SMP systems because they can run an application concurrently on all
computers in the cluster.
To take advantage to clustering, the application must be written specifically. This
involves a technique known as parallelization, which divides a program into
separate components that run in parallel on individual computers in the cluster.
Clustered system's usage and it's features should expand greatly as
SANs allow easy attachment of multiple hosts to multiple storage
units.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
33.
34. Operating-System Architecture
An operating system provides the environment within which
programs are executed.
One of the most important aspects of operating systems is the ability
to multiprogram. Multiprogramming increases CPU utilization by
organizing jobs (code and data) so that the CPU always has one to
execute.
The operating system keeps several jobs in memory simultaneously.
Since, in general, main memory is too small to accommodate all jobs,
the jobs are kept initially on the disk in the . This pool
consists of all processes residing on disk awaiting allocation of main
memory.
The operating system picks and begins to execute one of the jobs in
memory. When that job needs to wait, the CPU switches to another
job, and so on.
As long as at least one job needs to execute, the CPU is never idle.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
37. Operating-System Operations
Modern operating systems are interrupt driven. If there are no
processes to execute, no I/O devices to service, and no users to whom
to respond, an operating system will sit quietly, waiting for
something to happen.
Events are almost always signaled by the occurrence of an interrupt
or a trap.
A is a software-generated interrupt caused
either by an error (for example, division by zero or invalid memory
access) or by a specific request from a user program that an
operating-system service be performed.
A properly designed operating system must ensure that an incorrect
(or malicious) program cannot cause other programs to execute
incorrectly.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
38. In order to ensure the proper execution of the operating system, the
execution of operating-system code and user-defined code should be
distinguished.
Two separate modes of operation are required: and
(also called , , or
).
The processor switches between the two modes depending on what
type of code is running on the processor.
Applications run in user mode, and core operating system
components run in kernel mode.
Processes in user mode can access their own instructions and data,
but not kernel instructions and data. Processes in kernel mode, can
access kernel data and instructions as well as user data and
instructions.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
39. A bit, called the , is added to the hardware of the computer to
indicate the current mode: kernel (0) or user (1). With the mode bit, we can
distinguish between a task that is executed on behalf of the operating
system and one that is executed on behalf of the user.
When the computer system is executing on behalf of a user application, the
system is in user mode. However, when a user application requests a
service from the operating system (via a system call), the system must
transition from user to kernel mode to fulfill the request.
Operating Systems 14CS3503 Mukesh Chinta, Asst Prof, CSE, VRSEC
40. The dual mode of operation provides us with the means for
protecting the operating system from errant users—and errant users
from one another.
This protection is accomplished by designating some of the machine
instructions that may cause harm as privileged instructions
(examples include I/O control, timer management, and interrupt
management).
The hardware allows privilege instructions to be executed only in
kernel mode. If an attempt is made to execute a privileged
instruction in user mode, the hardware does not execute the
instruction but rather treats it as illegal and traps it to the operating
system.
CPUs that support virtualization frequently have a separate mode to
indicate when the virtual machine manager (VMM)—and the
virtualization management software—is in control of the system.
41. Timers are used to ensure that the operating system maintains
control over the CPU. It does not allow a user program get stuck in an
infinite loop and never return control to the OS.
A timer can be set to interrupt the computer after a specified period.
The period may be fixed (for example, 1/60 second) or variable (for
example, from 1 millisecond to 1 second).
A variable timer is generally implemented by a fixed-rate clock and a
counter. The operating system sets the counter.
Before turning over control to the user, the operating system ensures
that the timer is set to interrupt. If the timer interrupts, control
transfers automatically to the operating system, which may treat the
interrupt as a fatal error or may give the program more time. Clearly,
instructions that modify the content of the timer are privileged.
Timer is also used to prevent a user program from running too long.