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Operating System What is an Operating System?, Functions of an Operating System , Popular Operatinging Sysytem, What are the major differences between Unix and Linux? , iPhone Operating System (iOS) Service Models, Risks related to Cloud Computing, Disadvantages of Cloud Computing .


What is an Operating System?

An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

Functions of an Operating System

Following are some of important functions of an operating System:-

Memory Management
Processor Management
Device Management
File Management
Security
Control over system performance
Job accounting
Error detecting aids
Coordination between other software and users

Memory Management

Memory management refers to management of Primary Memory or Main Memory.
An Operating System does the following activities for memory management:
Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use.
In multiprogramming, the OS decides which process will get memory when and how much.
Allocates the memory when a process requests it to do so.
De-allocates the memory when a process no longer needs it or has been terminated.

Processor Management

In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling. An Operating System does the following activities for processor management:

Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller.
Allocates the processor (CPU) to a process.
De-allocates processor when a process is no longer required.

Device Management

An Operating System manages device communication via their respective drivers. It does the following activities for device management:

Keeps tracks of all devices. The program responsible for this task is known as the I/O controller.
Decides which process gets the device when and for how much time.
Allocates the device in the most efficient way.
De-allocates devices.

File Management

An Operating System does the following activities for file management:
Keeps track of information, location, uses, status etc. The collective facilities are often known as file system.
Decides who gets the resources.
Allocates the resources.
De-allocates the resources.

Other Important Activities

Security -- By means of password and similar other techniques, it prevents unauthorized access to programs and data.
Job accounting -- Keeping track of time and resources used by various jobs and users.
Error detecting aids -- Production of dumps, traces, error messages, and other debugging and error detecting aids.
Coordination between other software and users Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.

Popular Operatinging Sysytem

Android

Android is an operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers.

Android Software version history

Windows OS

Microsoft Windows (or simply Windows) is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft.
Windows 1.0 - Components included Calculator, Calendar, Clipboard viewer, Clock, Control Pannel, Notepad, Paint.
Windows 2.0 was released in December 1987, and was more popular than its predecessor. It features several improvements to the user interface and memory management.
Windows 2.03 changed the OS from tiled windows to overlapping windows.
Windows 3.x
First widely used successful version of Windows
Replaced MS-DOS
Windows 9x(windows 95)
was released on August 24, 1995
Introduced Start button, taskbar for multitasking, and My Computer for easier file management.
Windows 95 was a major commercial success for Microsoft.
Windows 95 was followed up with the release of Windows 98 on June 25, 1998,
In May 1999, Microsoft released Windows 98 Second Edition, an updated version of Windows 98.
Windows 98 SE added Internet Explorer 5.0 and Windows Media Player 6.2 amongst other upgrades
On September 14, 2000, Microsoft released Windows ME (Millennium Edition).  PC World considered Windows ME to be one of the worst operating systems Microsoft had ever released.
Windows NT
Intended for business computing
Increased reliability and security
Windows 2000
Security of NT with Windows 98 Interface
Windows 2000 Professional and Windows 2000 Server
The next major version of Windows NT, Windows XP, was released on October 25, 2001. 
Windows Vista
Windows Vista was released on November 30, 2006.
Windows 7
On July 22, 2009, Windows 7  was released.
Windows 8 and 8.1
Windows 8, the successor to Windows 7, was released generally on October 26, 2012.
An update to Windows 8, called Windows 8.1, was released on October 17, 2013.
On September 30, 2014, Microsoft announced  Windows 10 as the successor to Windows 8.1. It was released on July 29, 2015

What are the major differences between Unix and Linux?

That's a very broad question and could be answered any number of ways.
Probably the simplest answer is that from a technical point of view there are no major differences.
Most people aren't satisfied with believing that Linux and UNIX are very similar, though.
Here's a list of the most obvious remaining differences.
Unix is a commercial product where as Linux is a freeware.
Those who sale Linux do not actually charge for Linux but for the support they provide.
There are few minor differences between Unix & Linux.
Unix is a commercial product where as Linux is a freeware.
Those who sale Linux do not actually charge for Linux but for the support they provide.
There are few minor differences between Unix & Linux.

iPhone Operating System (iOS)

What is iOS?(iOS)

Apples mobile operating system considered the foundation of the iPhone
Originally designed for the iPhone but now supports iPod touch, iPad, and Apple TV
It is updated just like Itune for iPods
As of Oct 2011 Apple contains over 500,000 iOS applications.

History

iPhone OS was first unveiled in Jan 2007 at the Macworld Conference and Expo Released June 2007
In June 2010 licensed the trademark iOS (From Cisco IOS)
Now goes all the way up to iOS 10.
Originally did not allow third party applications but after Feb 2008 this changed.

What is Google Chrome ?

Google Chrome is a freeware web browser developed by Google.It was first released in September 2008, for Microsoft Windows, and was later ported to Linux, macOS, iOS and Android. Google Chrome is also the main component of Chrome OS, where it serves as a platform for running web apps.
Google releases the majority of Chrome's source code as the Chromium open-source project.
One component that is not open-source is the built-in Adobe Flash Player (that Chrome has disabled by default since September 2016.Chrome used the WebKit layout engine until version 27. As of version 28, all Chrome ports except the iOS port use Blink, a fork of the WebKit engine
As of Q2 2017, StatCounter estimates that Google Chrome has a 63% worldwide usage share of web browsers as a desktop browser.It also has 54% market share across all platforms combined,because it is also the most popular browser for smartphones. Its success has led to Google expanding the "Chrome" brand name on various other products such as Chromecast, Chromebook, Chromebit, Chromebox and Chromebase.

Cloud Computing

What is Cloud?

The term Cloud refers to a Network.
In other words, we can say that Cloud is something, which is present at remote location.
Cloud can provide services over public and private networks, i.e., WAN, LAN or VPN.
Cloud Computing refers to manipulating, configuring, and accessing the hardware and software resources remotely. It offers online data storage, infrastructure, and application.

Working Models

There are certain services and models working behind the scene making the cloud computing feasible and accessible to end users. Following are the working models for cloud computing:
There are certain services and models working behind the scene making the cloud computing feasible and accessible to end users. Following are the working models for cloud computing:
-Deployment Models
-Service Models

Deployment Models

Public Cloud

The public cloud allows systems and services to be easily accessible to the general public. Public cloud may be less secure because of its openness.

Unemployed

The public cloud allows systems and services to be easily accessible to the general public. Public cloud may be less secure because of its openness.

Private Cloud
The private cloud allows systems and services to be accessible within an organization. It is more secured because of its private nature.
Community Cloud
The community cloud allows systems and services to be accessible by a group of organizations.
Hybrid Cloud
The hybrid cloud is a mixture of public and private cloud, in which the critical activities are performed using private cloud while the non-critical activities are performed using public cloud.

Service Models

There are three service models such as:
Infrastructure-as–a-Service (IaaS)
Platform-as-a-Service (PaaS)
Software-as-a-Service (SaaS)

Infrastructure-as-a-Service (IaaS)

There are three service models such as

The Infrastructure-as-a-Service (IaaS) is the most basic level of service.
IaaS provides access to fundamental resources such as physical machines, virtual machines, virtual storage, etc.
Example -
Amazon S3, Dell, Apple, ...

PLATFORM-AS-A-SERVICE (PAAS)

There are three service models such as

PaaS provides the runtime environment for applications, development and deployment tools, etc.

Example -
Application platform - Google App Engine, Mosso, Force.com, Engine Yard,Facebook, Heroku, AWS

Storage Platform - 3Tera, EC2, SliceHost, GoGrid, RightScale, Linode

SOFTWARE-AS-A-SERVICE (SAAS)

There are three service models such as
SaaS model allows to use software applications as a service to end-users.
Example –
MS Live/ExchangeLabs, IBM, Google Apps; Salesforce.com, Quicken Online, Zoho, Cisco

Advantages of Cloud Computing

There are three service models such as

Lower computer costs:

1.You do not need a high-powered and high-priced computer to run cloud computing's web-based applications.

2.Since applications run in the cloud, not on the desktop PC, your desktop PC does not need the processing power or hard disk space demanded by traditional desktop software.

Improved performance:

1.Computers in a cloud computing system boot and run faster because they have fewer programs and processes loaded into memory…

Reduced software costs:

1.Instead of purchasing expensive software applications, you can get most of what you need for free-ish!

Instant software updates:

1.Another advantage to cloud computing is that you are no longer faced with choosing between obsolete software and high upgrade costs.

Risks related to Cloud Computing

1.Security and Privacy - It is the biggest concern about cloud computing. Since data management and infrastructure management in cloud is provided by third-party, it is always a risk to handover the sensitive information to cloud service providers.

2.Lock In - It is very difficult for the customers to switch from one Cloud Service Provider (CSP) to another. It results in dependency on a particular CSP for service.

3.Insecure or Incomplete Data Deletion - It is possible that the data requested for deletion may not get deleted.

Disadvantages of Cloud Computing

1.Requires a constant Internet connection:

Cloud computing is impossible if you cannot connect to the Internet.

Since you use the Internet to connect to both your applications and documents, if you do not have an Internet connection you cannot access anything, even your own documents.

A dead Internet connection means no work and in areas where Internet connections are few or inherently unreliable, this could be a deal-breaker.

2.Does not work well with low-speed connections:

Similarly, a low-speed Internet connection, such as that found with dial-up services, makes cloud computing painful at best and often impossible.

Web-based applications require a lot of bandwidth to download, as do large documents.

3.Can be slow:

Even with a fast connection, web-based applications can sometimes be slower than accessing a similar software program on your desktop PC.

Everything about the program, from the interface to the current document, has to be sent back and forth from your computer to the computers in the cloud.