Abstract a general term for anything that involves delivering

 Abstract
Attempts are made in this paper to define Cloud Computing first, then identify the different types of it.  We move to discuss the basic requirement of Cloud in the next section and  finally the advantages  and disadvantages of Cloud computing  are analyzed. It is clarified that Cloud Computing is a virtualized compute power and storage delivered via platform-agnostic infrastructures of abstracted hardware and software accessed over the Internet. These shared, on-demand IT resources, are created and disposed of efficiently, are dynamically scalable through a variety of programmatic interfaces and are billed variably based on measurable usage.
A cloud can be private or public. A public cloud sells services to anyone on the Internet. (Currently, Amazon WebServices is the largest public cloud provider.) A private cloud is a proprietary network or a data center that supplies hosted services to a limited number of people. 
Clod Computing provides services as follows: i-Infrastructure as a services (IaaS) ii-Platform as a services (PaaS) and Software as a Services (SaaS). The  layers and infrastructure of cloud computing as well as its advantages and dis advantages are discussed in the following sections.

Key Words: Cloud Computing, Virtual Server, LaaS, Paps, SaaS.

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1- Definitions
Cloud computing is a general term for anything that involves delivering hosted services over the Internet.These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS),Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). The name cloud computing was inspired by the cloud symbol thats often used to represent the Internet in flowcharts and diagrams. When a service provider uses public cloud resources to create their private cloud, the result is called a virtual private cloud. Private or public, the goal of cloud computing is to provide easy, scalable access to computing resources and IT services.  to start, stop, access and configure their virtual servers and storage. In the enterprise, cloud computing allows a company to pay for only as much capacity as is needed, and bring more online as soon as required.Because this pay-for-what-you-use model resembles the way electricity, fuel and water are consumed, its sometimes referred to as utility computing.
Platform-as-a-service in the cloud is defined as a set of software and product development tools hosted on the providers infrastructure. Developers create applications on the providers platform over the Internet. Paas providers may use APIs, website portals or gateway software installed on the customers computer. Force.com, (an outgrowth of Salesforce.com) and GoogleApps are examples of PaaS. Developers need to know that currently, there are not standards for interoperability or data portability in the cloud. Some providers will not allow software created by their customers to be moved off the providers platform.
In the software-as-a-service cloud model, the vendor supplies the hardware infrastructure, the software product and interacts with the user through a front-end portal. SaaS is a very broad market.Services can be anything from Web-based email to inventory control and database processing. Because the service provider hosts both the application and the data, the end user is free to use the service from anywhere.
Cloud computing is a general term for anything that involves delivering hosted services over the Internet. These services are broadly divided into three categories: Infrastructure-as-a-Service (IaaS),Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). The name cloud computing was inspired by the cloud symbol thats often used to represent the Internet in flowcharts and diagrams.
2- Different Types of Cloud Computing:
. Public Cloud: Computing infrastructure is hosted at the vendor’s premises. The customer has no visibility over the location of the cloud computing infrastructure. The computing infrastructure is shared between organizations.
Private Cloud: Computing architecture is dedicated to the customer and is not shared with other organizations. They are expensive and are considered more secure than Public Clouds.Private clouds may be externally hosted ones as well as in premise hosted 
Hybrid Cloud: Organizations host some critical, secure applications in private clouds.The not so critical applications are hosted in the public cloud.The combination is known as Hybrid Cloud. Cloud bursting is the term used to define a system where the organization uses its own infrastructure for normal usage, but cloud is used for peak loads.
Community Cloud: The cloud infrastructure is shared between the organizations of the same community. For example, all the government agencies in a city can share the same cloud but not the non government agencies.
3-Layers
Once an internet protocol connection is established among several computers, it is possible to share services within anyone of the following layers.
a-Client
A cloud client consists of computer hardware and/or computer software that relies on cloud computing for application delivery and that is in essence useless without it. Examples include some computers (example: Chromebook), phones (example:Google Nexus series) and other devices, operating systems (example: GoogleChrome OS), and browsers.
b-Application
Cloud application services or “Softwares as a Service (SaaS)” deliver software as a service over the Internet, eliminating the need to install and run the application on the customers own computers and simplifying maintenance and support.
c-Platform 
Cloud platform services, also known as platform as a service (PaaS), deliver a computing platform and/or solution stack as a service, often consuming cloud infrastructure and sustaining cloud applications. It facilitates deployment of applications without the cost and complexity of buying and managing the underlying hardware and software layers.Cloud computing is becoming a major change in our industry, and one of the most important parts of this change is the shift of cloud platforms. Platforms let developers write certain applications that can run in the cloud, or even use services provided by the cloud. There are different names being used for platforms which can include the on-demand platform, or Cloud 9. Its your choice on what you would like to call the platform, but they all have great potential in developing.When development teams create applications for the cloud, they must build its own cloud platform.
d-Infrastructure
Cloud infrastructure services, also known as “infrastructure as a service”(IaaS), deliver computer infrastructure –typically a platform virtualization environment – as a service, along with raw (block) storage and networking.Rather than purchasing servers, software, data-center space or network equipment, clients instead buy those resources as a fully outsourced service.Suppliers typically bill such services on a utility computing basis; the amount of resources consumed (and therefore the cost) will typically reflect the level of activity.
e-Server
The servers layer consists of computer hardware and/or computer software products that are specifically designed for the delivery of cloud services, including multi-core processors, cloud-specific operating systems and combined offerings.
 4- Advantages and Disadvantages of Cloud Computing in a General:
 • Lower computer costs: You do not need a high-powered and high-priced computer to run cloud computings web-based applications.
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: With few large programs hogging your computers memory, you will see better performance from your PC.
Computers in a cloud computing system boot and run faster because they have fewer programs and processes loaded into memory…
• Reduced software costs:
 Instead of purchasing expensive software applications, you can get most of what you need for free!
is right – most cloud computing applications today, such as the Google Docs suite, are totally free.

That is a lot better than paying $200+ for similarMicrosoft Office software
which alone may be justification for switching to cloud applications
• Instant software updates:
Another advantage to cloud computing is that you are no longer faced with choosing between obsolete software and high upgrade costs.
When the application is web-based, updates happen automatically -available the next time you log into the cloud.
 When you access a web-based application, you get the latest version -without needing to pay for or download an upgrade.
• Improved document format compatibility.
You do not have to worry about the documents you create on your machine being compatible with other users applications or operating systems.Where Word 2007 documents cannot be opened on a computer running Word 2003, all documents can be read!There are potentially no format incompatibilities when everyone is sharing documents and applications in the cloud
• Unlimited storage capacity:
 Cloud computing offers virtually limitless storage. 
 Your computers current200 Gbyte hard drive is small compared to the hundreds of Bytes available in the cloud.
 Whatever you need to store, you can.
• Increased data reliability:
 Unlike desktop computing, in which if a hard disk crashes and destroy all your valuable data, a computer crashing in the cloud should not affect the storage of your data.
 That also means that if your personal computer crashes, all your data is still out there in the cloud, still accessible.
 In a world where few individual desktop PC users back up their data on a regular basis, cloud computing is a data-safe computing platform!
• Universal document access:
 That is not a problem with cloud computing, because you do not take your documents with you.
 Instead, they stay in the cloud, and you can access them whenever you have a computer and an Internet connection.
All your documents are instantly available from wherever you are.
• Latest version availability:
 Another document-related advantage of cloud computing is that when you edit a document at home, that edited version is what you see when you access the document at work.
The cloud always hosts the latest version of your documents; as long as you are connected, you are not in danger of having an outdated version
• Easier group collaboration:
 Sharing documents leads directly to better collaboration.
 Many users do this as it is an important advantages of cloud computing -multiple users can collaborate easily on documents and projects.
 Because the documents are hosted in the cloud, not on individual computers, all you need is an Internet connection, and you are collaborating.
• Device independence:
 You are no longer tethered to a single computer or network.
 Changes to computers, applications and documents follow you through the cloud.
 Move to a portable device, and your applications and documents are still available.
Disadvantages of Cloud Computing
• 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 no 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.When you are offline, cloud computing simply does not work.
• 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. If the cloud servers happen to be backed up at that moment, or if the Internet is having a slow day, you would not get the instantaneous access you might expect from desktop applications.
• Features might be limited:
This situation is bound to change, but today many web-based applications simply are not as full-featured as their desktop-based applications.
 For example, you can do a lot more with Microsoft PowerPoint than with Google Presentations web-based offering.
 The basics are similar, but the cloud application lacks many of PowerPoints advanced features.
 If you are a power user, you might not want to leap into cloud computing just yet.
• HPC Systems: Not clear that you can run compute-intensive HPC applications that use MPI/OpenMP!– Scheduling is important with this type of application – as you want all the VM to be co-located to mini mise communication latency!
• General Concerns:
Each cloud systems uses different protocols and different APIs… so it may not be possible to run applications between cloud based systems.
Amazon has created its own DB system (not SQL92), and workflow system(many popular workflow systems out there) – so your normal applications will have to be adapted to execute on these platforms.
The Future
Many of the activities loosely grouped together under cloud computing have already been happening and centralized computing activity is not a new phenomena:
• Grid Computing was the last research-led centralized approach.
• However there are concerns that the mainstream adoption of cloud computing could cause many problems for users.
• Whether these worries are grounded or not has yet to be seen.
• Many new open source systems appearing that you can install and run on your local cluster – should be able to run a variety of applications on these systems.
Advantages and Disadvantages According to Layers
SaaS resides here
Most common Cloud / Many providers of different services
Examples: SalesForce, Gmail, Yahoo! Mail, Quicken Online
Advantages: Free, Easy,Consumer Adoption
Disadvantages: Limited functionality, no control or access to underlying technology
Cloud “Platforms”
“Containers”
“Closed” environments
Examples: Google App Engine, Heroku, Mosso, Engine Yard,J oyent or Force.com (SalesForceDev Platform)
Advantages: Good for developers, more control than”Application” Clouds, tightly configured
Disadvantages: Restricted to what is available, other dependencies
Cloud “Infrastructure
Provide “Compute” and”Storage” clouds
Virtualization layers(hardware/software)
Examples: Amazon EC2,GoGrid, Amazon S3, Nirvanix, Linode
Advantages: Full control of environments and infrastructure
Disadvantages: premium price point, limited competition
Cloud “Extenders” (Wild Card)
Provides extension to Cloud Infrastructure and Platforms with basic functionality 
Examples: Amazon SimpleDB,Amazon SQS, Google BigTable
Advantages: Extends functionality of Compute & Storage Clouds to integrate with legacy system or other clouds
Disadvantages: Sometimes requires use of specific Platforms or Infrastructure
Cloud “Aggregators” (Wild Card)
Sits on top of various Cloud Infrastructures for management
Advantages: Provides more options for Cloud environments
Disadvantages: Dependent onCloud Providers
6-CONCLUSION:
Finally, cloud apps don’t eat up your valuable IT resources, so your CFO will love it. This lets you focus on deploying more apps, new projects, and innovation.Cloud computing is a simple idea, but it can have a huge impact on your business.

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