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Cloud Computing is Internet-based computing, whereby shared resources,software, and information are provided to computers and other devices ondemand, like the electricity grid.

Cloud computing is a paradigm shift following the shift from mainframe toclient–server in the early 1980s. Details are abstracted from the users, whono longer have need for expertise in, or control over, the technologyinfrastructure "in the cloud" that supports them.[1] Cloud computingdescribes a new supplement, consumption, and delivery model for ITservices based on the Internet, and it typically involves over-the-Internet 

 provision of dynamically scalable and often virtualized resources.[2][3] It is a byproduct and consequence of the ease-of-access to remote computing sites provided by the Internet.[4]

The term "cloud" is used as a metaphor for the Internet, based on the clouddrawing used in the past to represent the telephone network,[5] and later todepict the Internet in computer network diagrams as an abstraction of theunderlying infrastructure it represents.[6] Typical cloud computing providersdeliver common business applications online that are accessed from another Web service or software like a Web browser , while the software and data arestored on servers.

Most cloud computing infrastructures consist of services delivered throughcommon centers and built on servers. Clouds often appear as single points of 

access for all consumers' computing needs. Commercial offerings aregenerally expected to meet quality of service (QoS) requirements of customers, and typically include SLAs.[7] The major cloud service providersinclude Microsoft,[8] Salesforce, Skytap, HP, IBM, Amazon and Google.[9][10]

Comparisons

Cloud computing derives characteristics from, but should not be confusedwith:

1. Autonomic computing — "computer systems capable of self-management".[11] 

2. Client–server model – Client–server computing refers broadly to anydistributed application that distinguishes between service providers(servers) and service requesters (clients).[12] 

3. Grid computing — "a form of distributed computing and parallelcomputing, whereby a 'super and virtual computer' is composed of a

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cluster of networked, loosely coupled computers acting in concert to perform very large tasks"

4. Mainframe — powerful computers used mainly by large organizationsfor critical applications, typically bulk data processing such as census,industry and consumer statistics, enterprise resource planning, andfinancial transaction processing.[13] 

5. Utility computing — the "packaging of computing resources, such ascomputation and storage, as a metered service similar to a traditional

 public utility, such as electricity";[14] 6. Peer-to-peer  – a distributed architecture without the need for central

coordination, with participants being at the same time both suppliersand consumers of resources (in contrast to the traditional client–server model).

Characteristics

In general, Cloud computing customers do not own the physicalinfrastructure, instead avoiding capital expenditure by renting usage from athird-party provider. They consume resources as a service and pay only for resources that they use. Many cloud-computing offerings employ the utilitycomputing model, which is analogous to how traditional utility services(such as electricity) are consumed, whereas others bill on a subscription 

 basis. Sharing "perishable and intangible" computing power among multipletenants can improve utilization rates, as servers are not unnecessarily left

idle (which can reduce costs significantly while increasing the speed of application development). A side-effect of this approach is that overallcomputer usage rises dramatically, as customers do not have to engineer for 

 peak load limits.[15] In addition, "increased high-speed bandwidth" makes it possible to receive the same response times from centralized infrastructure atother sites

Economics

Cloud computing users can avoid capital expenditure (CapEx) on hardware,software, and services when they pay a provider only for what they use.Consumption is usually billed on a utility (resources consumed, likeelectricity) or subscription (time-based, like a newspaper) basis with little or no upfront cost. Other benefits of this time sharing-style approach are low

 barriers to entry, shared infrastructure and costs, low management overhead,and immediate access to a broad range of applications. In general, users can

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terminate the contract at any time (thereby avoiding return on investment risk and uncertainty), and the services are often covered by service levelagreements (SLAs) with financial penalties.

According to Nicholas Carr , the strategic importance of informationtechnology is diminishing as it becomes standardized and less expensive. Heargues that the cloud computing paradigm shift is similar to the displacementof electricity generators by electricity grids early in the 20th century.[18]

Although companies might be able to save on upfront capital expenditures,they might not save much and might actually pay more for operatingexpenses. In situations where the capital expense would be relatively small,or where the organization has more flexibility in their capital budget thantheir operating budget, the cloud model might not make great fiscal sense.

Other factors impacting the scale of any potential cost savings include theefficiency of a company's data center as compared to the cloud vendor's, thecompany's existing operating costs, the level of adoption of cloudcomputing, and the type of functionality being hosted in the cloud.[19][20]

Among the items that some cloud hosts charge for are instances (often withextra charges for high-memory or high-CPU instances); data transfer in andout; storage (measured by the GB-month); I/O requests; PUT requests andGET requests; IP addresses; and load balancing. In some cases, users can bidon instances, with pricing dependent on demand for available instances.[citation

needed ]

Architecture

Cloud computing sample architecture

Cloud architecture,[21] the systems architecture of the software systems involved in the delivery of cloud computing , typically involves multiple

cloud components communicating with each other over application programming interfaces, usually web services.[22] This resembles the Unix philosophy of having multiple programs each doing one thing well andworking together over universal interfaces. Complexity is controlled and theresulting systems are more manageable than their monolithic counterparts.

History

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The underlying concept of cloud computing dates back to 1960s, when JohnMcCarthy opined that "computation may someday be organized as a publicutility". Almost all the modern day characteristics of cloud computing(elastic provision, provided as a utility, online, illusion of infinite supply),the comparison to the electricity industry and the use of public, private,government and community forms was thoroughly explored in DouglasParkhill's, 1966 book, "The Challenge of the Computer Utility".

The actual term "cloud" borrows from telephony in that telecommunicationscompanies, who until the 1990s primarily offered dedicated point-to-pointdata circuits, began offering Virtual Private Network (VPN) services withcomparable quality of service but at a much lower cost. By switching trafficto balance utilization as they saw fit they were able to utilise their overallnetwork bandwidth more effectively. The cloud symbol was used to denote

the demarcation point between that which was the responsibility of the provider from that of the user. Cloud computing extends this boundary tocover servers as well as the network infrastructure.[23]

Amazon played a key role in the development of cloud computing bymodernizing their data centers after the dot-com bubble, which, like mostcomputer networks, were using as little as 10% of their capacity at any onetime just to leave room for occasional spikes. Having found that the newcloud architecture resulted in significant internal efficiency improvementswhereby small, fast-moving "two-pizza teams" could add new features faster 

and easier, Amazon started providing access to their systems throughAmazon Web Service (AWS) on a utility computing basis in 2006.[24]

In 2007, Google, IBM, and a number of universities embarked on a largescale cloud computing research project.[25] In early 2008, Eucalyptus becamethe first open source AWS API compatible platform for deploying privateclouds. By mid-2008, Gartner saw an opportunity for cloud computing "toshape the relationship among consumers of IT services, those who use ITservices and those who sell them",[26] and observed that "[o]rganisations are

switching from company-owned hardware and software assets to per-useservice-based models" so that the "projected shift to cloud computing ... willresult in dramatic growth in IT products in some areas and significantreductions in other areas."[27]

Key features

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• Agility improves with users' ability to rapidly and inexpensively re- provision technological infrastructure resources. [28] 

• Cost is claimed to be greatly reduced and capital expenditure isconverted to operational expenditure[29]  . This ostensibly lowers

 barriers to entry, as infrastructure is typically provided by a third- party and does not need to be purchased for one-time or infrequentintensive computing tasks. Pricing on a utility computing basis is fine-grained with usage-based options and fewer IT skills are required for implementation (in-house).[30] 

• Device and location independence[31] enable users to access systemsusing a web browser regardless of their location or what device theyare using (e.g., PC, mobile). As infrastructure is off-site (typically

 provided by a third-party) and accessed via the Internet, users canconnect from anywhere.[30] 

• Multi-tenancy enables sharing of resources and costs across a large pool of users thus allowing for:

o Centralization of infrastructure in locations with lower costs(such as real estate, electricity, etc.)

o Peak-load capacity increases (users need not engineer for highest possible load-levels)

o Utilization and efficiency improvements for systems that areoften only 10–20% utilized.[24] 

• Reliability is improved if multiple redundant sites are used, whichmakes well designed cloud computing suitable for  business continuity and disaster recovery.[32] Nonetheless, many major cloud computingservices have suffered outages, and IT and business managers can attimes do little when they are affected.[33][34] 

• Scalability via dynamic ("on-demand") provisioning of resources on afine-grained, self-service basis near real-time, without users having toengineer for peak loads. Performance is monitored, and consistent andloosely coupled architectures are constructed using web services asthe system interface.[30] One of the most important new methods for overcoming performance bottlenecks for a large class of applications

is data parallel programming on a distributed data grid.[35] • Security could improve due to centralization of data[36], increased

security-focused resources, etc., but concerns can persist about loss of control over certain sensitive data, and the lack of security for storedkernels[37]. Security is often as good as or better than under traditionalsystems, in part because providers are able to devote resources tosolving security issues that many customers cannot afford.[38] 

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Providers typically log accesses, but accessing the audit logs themselves can be difficult or impossible. Furthermore, thecomplexity of security is greatly increased when data is distributedover a wider area and / or number of devices.

• Maintenance cloud computing applications are easier to maintain,since they don't have to be installed on each user's computer. They areeasier to support and to improve since the changes reach the clientsinstantly.

• Metering cloud computing resources usage should be measurable andshould be metered per client and application on daily, weekly,monthly, and annual basis. This will enable clients on choosing thevendor cloud on cost and reliability (QoS).

Layers

Client

See also: Category:Cloud clients

A cloud client consists of computer hardware and/or computer software thatrelies on cloud computing for application delivery, or that is specificallydesigned for delivery of cloud services and that, in either case, is essentially

useless without it. Examples include some computers, phones and other devices, operating systems and browsers.[39][40][41][42][43]

Application

See also: Category:Cloud applications

Cloud application services or "Software as a Service (SaaS)" deliver software as a service over the Internet, eliminating the need to install and run theapplication on the customer's own computers and simplifying maintenance

and support. Key characteristics include:[44]

•  Network-based access to, and management of, commercially available(i.e., not custom) software

• Activities that are managed from central locations rather than at eachcustomer's site, enabling customers to access applications remotelyvia the Web

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• Application delivery that typically is closer to a one-to-many model(single instance, multi-tenant architecture) than to a one-to-one model,including architecture, pricing, partnering, and managementcharacteristics

• Centralized feature updating, which obviates the need for downloadable patches and upgrades.

Platform

See also: Category:Cloud platforms

Cloud platform services or " Platform as a Service (PaaS)" deliver acomputing platform and/or solution stack as a service, often consumingcloud infrastructure and sustaining cloud applications.[45] It facilitates

deployment of applications without the cost and complexity of buying andmanaging the underlying hardware and software layers.[46][47]

Infrastructure

See also: Category:Cloud infrastructure

Cloud infrastructure services or " Infrastructure as a Service (IaaS)" deliverscomputer  infrastructure, typically a platform virtualization environment as aservice. Rather than purchasing servers, software, data center space or 

network equipment, clients instead buy those resources as a fully outsourcedservice. The service is typically billed on a utility computing basis andamount of resources consumed (and therefore the cost) will typically reflectthe level of activity. It is an evolution of virtual private server offerings. [48]

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.[39][49][50][51]

Deployment models

Cloud computing types

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Public cloud

 Public cloud or external cloud describes cloud computing in the traditionalmainstream sense, whereby resources are dynamically provisioned on a fine-grained, self-service basis over the Internet, via web applications/webservices, from an off-site third-party provider who shares resources and billson a fine-grained utility computing basis.[30]

Community cloud

A community cloud may be established where several organizations havesimilar requirements and seek to share infrastructure so as to realize some of the benefits of cloud computing. With the costs spread over fewer users thana public cloud (but more than a single tenant) this option is more expensive

 but may offer a higher level of privacy, security and/or policy compliance.Examples of community cloud include Google's "Gov Cloud".[52]

Hybrid cloud

See also: Cloud storage gateway

A hybrid cloud environment consisting of multiple internal and/or external providers[53] "will be typical for most enterprises".[54] By integrating multiplecloud services users may be able to ease the transition to public cloud 

services while avoiding issues such as PCI compliance.[55]

Another perspective on deploying a web application in the cloud is usingHybrid Web Hosting, where the hosting infrastructure is a mix betweenCloud Hosting for the web server, and Managed dedicated server for thedatabase server.

Private cloud

The concept of a Private Computer Utility was first described by Douglas

Parkhill in his 1966 book "The Challenge of the Computer Utility". The ideawas based upon direct comparison with other industries (e.g. the electricityindustry) and the extensive use of hybrid supply models to balance andmitigate risks.

 Private cloud and internal cloud have been described as neologisms,however the concepts itself pre-dates the term cloud by 40 years. Even

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within modern utility industries, hybrid models still exist despite theformation of reasonably well functioning markets and the ability to combinemultiple providers.

Some vendors have used the terms to describe offerings that emulate cloudcomputing on private networks. These (typically virtualisation automation)

 products offer the ability to deliver some benefits of cloud computing whilstmitigating some of the pitfalls. These offerings capitalise on data security,corporate governance, and reliability concerns during this time of transitionfrom a product to a functioning service based industry supported bycompetitive marketplaces.

They have been criticized on the basis that users "still have to buy, build,and manage them" and as such do not benefit from lower up-front capital

costs and less hands-on management[54]

, essentially "[lacking] the economicmodel that makes cloud computing such an intriguing concept".[56][57]

Cloud Storage

Main article: Cloud Storage

Cloud Storage is a model of networked Computer data storage where data isstored on multiple virtual servers, generally hosted by third parties, rather than being hosted on dedicated servers. Hosting companies operate large

data centers; and people who require their data to be hosted buy or leasestorage capacity from them and use it for their storage needs. The data center  operators, in the background, virtualize the resources according to therequirements of the customer and expose them as virtual servers, which thecustomers can themselves manage. Physically, the resource may span acrossmultiple servers.

The Intercloud

Main article: Intercloud

The Intercloud[58]  is an interconnected global "cloud of clouds"[59][60] and anextension of the Internet "network of networks" on which it is based[61]. Theterm was first used in the context of cloud computing in 2007 when KevinKelly opined that "eventually we'll have the intercloud, the cloud of clouds.This Intercloud will have the dimensions of one machine comprising all

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servers and attendant cloudbooks on the planet."[59]. It became popular in2009[62] and has also been used to describe the datacenter of the future[63].

The Intercloud scenario is based on the key concept that each single clouddoes not have infinite physical resources. If a cloud saturates thecomputational and storage resources of its virtualization infrastructure, itcould not be able to satisfy further requests for service allocations sent fromits clients. The Intercloud scenario aims to address such situation, in fact,each cloud can use the computational and storage resources of thevirtualization infrastructures of other clouds. Such form of pay-for-useintroduces new business opportunities among cloud providers. Nevertheless,the Intercloud raises many challenges concerning cloud federation, security,interoperability, QoS, monitoring and billing

The concept of a competitive utility computing market which combinedmany computer utilities together was originally described by DouglasParkhill in his 1966 book, the "Challenge of the Computer Utility". Thisconcept has been subsequently used many times over the last 40 years and isidentical to the "InterCloud".

Issues

Privacy

The Cloud model has been criticized by privacy advocates for the greater ease in which the companies hosting the Cloud services control, and thus,can monitor at will, lawfully or unlawfully, the communication and datastored between the user and the host company. Instances such as the secret

 NSA program, working with AT&T, and Verizon, which recorded over 10million phone calls between American citizens, causes uncertainty among

 privacy advocates, and the greater powers it gives to telecommunicationcompanies to monitor user activity.[64] While there have been efforts (such asUS-EU Safe Harbor ) to "harmonise" the legal environment, providers suchas Amazon still cater to major markets (typically the United States and theEuropean Union) by deploying local infrastructure and allowing customersto select "availability zones."[65]

Compliance

In order to obtain compliance with regulations including FISMA, HIPAA and SOX in the United States, the Data Protection Directive in the EU and

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the credit card industry's PCI DSS, users may have to adopt community or hybrid deployment modes which are typically more expensive and may offer restricted benefits. This is how Google is able to "manage and meetadditional government policy requirements beyond FISMA"[66][67] andRackspace Cloud are able to claim PCI compliance.[68] Customers in the EUcontracting with Cloud Providers established outside the EU/EEA have toadhere to the EU regulations on export of personal data[69].

Many providers also obtain SAS 70 Type II certification (e.g. Amazon[70],Salesforce.com[71], Google[72] and Microsoft[73]), but this has been criticisedon the grounds that the hand-picked set of goals and standards determined

 by the auditor and the auditee are often not disclosed and can vary widely.[74]

Providers typically make this information available on request, under non-disclosure agreement.[75]

Legal

In March 2007, Dell applied to trademark the term "cloud computing" (U.S.Trademark 77,139,082) in the United States. The "Notice of Allowance" thecompany received in July 2008 was cancelled in August, resulting in aformal rejection of the trademark application less than a week later.

Since 2007, the number of trademark filings covering cloud computing brands, goods and services has increased at an almost exponential rate. As

companies sought to better position themselves for cloud computing branding and marketing efforts, cloud computing trademark filings increased by 483% between 2008 and 2009. In 2009, 116 cloud computing trademarkswere filed, and trademark analysts predict that over 500 such marks could befiled during 2010.[76]

Open source

Open source software has provided the foundation for many cloudcomputing implementations.[77] In November 2007, the Free Software

Foundation released the Affero General Public License, a version of GPLv3 intended to close a perceived legal loophole associated with free software designed to be run over a network.[78]

Open standards

See also: Category:Cloud standards

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Open standards are critical to the growth of cloud computing. Most cloud providers expose APIs which are typically well-documented (often under aCreative Commons license[79]) but also unique to their implementation andthus not interoperable. Some vendors have adopted others' APIs[80] and thereare a number of open standards under development, including the OGF'sOpen Cloud Computing Interface. The Open Cloud Consortium (OCC) [81] isworking to develop consensus on early cloud computing standards and

 practices.

Security

Main article: Cloud computing security

The relative security of cloud computing services is a contentious issue

which may be delaying its adoption.

[82]

Some argue that customer data ismore secure when managed internally, while others argue that cloud providers have a strong incentive to maintain trust and as such employ ahigher level of security.[83]

The Cloud Security Alliance is a non-profit organization formed to promotethe use of best practices for providing security assurance within CloudComputing. [84]

Availability and Performance

In addition to concerns about security, businesses are also worried aboutacceptable levels of availability and performance of applications hosted inthe cloud.[85]

There are also concerns about a cloud provider shutting down for financialor legal reasons, which has happened in a number of cases. [86]

Sustainability

Although cloud computing is often assumed to be a form of "greencomputing", there is as of yet no published study to substantiate thisassumption. [87]

Research

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A number of universities, vendors and government organizations areinvesting in research around the topic of cloud computing.[88] Academicinstitutions include University of Melbourne (Australia), Georgia Tech,Yale, Wayne State, Virginia Tech, University of Wisconsin Madison,Boston University, Carnegie Mellon, MIT, Indiana University, University of Massachusetts, University of Maryland, North Carolina State, Purdue,University of California, University of Washington, University of Virginia,University of Utah, University of Minnesota, among others.[89]

Joint government, academic and vendor collaborative research projectsinclude the IBM/Google Academic Cloud Computing Initiative (ACCI). InOctober 2007 IBM and Google announced the multi- university projectdesigned to enhance students' technical knowledge to address the challengesof cloud computing.[90] In April 2009, the National Science Foundation 

 joined the ACCI and awarded approximately $5 million in grants to 14academic institutions.[91]

In July 2008, HP, Intel Corporation and Yahoo! announced the creation of aglobal, multi-data center, open source test bed, called Open Cirrus[92],designed to encourage research into all aspects of cloud computing, serviceand data center management.[93] Open Cirrus partners include the NSF, theUniversity of Illinois (UIUC), Karlsruhe Institute of Technology, theInfocomm Development Authority (IDA) of Singapore, the Electronics andTelecommunications Research Institute (ETRI) in Korea, the Malaysian

Institute for Microelectronic Systems(MIMOS), and the Institute for SystemProgramming at the Russian Academy of Sciences (ISPRAS).[94]

In July 2010, HP Labs India announced a new cloud-based technologydesigned to simplify taking content and making it mobile-enabled, evenfrom low-end devices.[95] Called SiteonMobile, the new technology isdesigned for emerging markets where people are more likely to access theinternet via mobile phones rather than computers.[96]

The IEEE Technical Committee on Services Computing[97] in IEEEComputer Society sponsors the IEEE International Conference on CloudComputing (CLOUD)[98]. CLOUD 2010 was held on July 5–10, 2010 inMiami, Florida.

Criticism of the term

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This article's Criticism or Controversy section(s) may mean the article

does not present a neutral point of view of the subject. It may be better to integrate the material in those sections into the article as a whole.(March 2010)

During a video interview, Forrester Research VP Frank Gillett expressescriticism about the nature of and motivations behind the push for cloudcomputing. He describes what he calls "cloud washing" in the industrywhereby companies relabel their products as cloud computing resulting in alot of marketing innovation on top of real innovation. The result is a lot of overblown hype surrounding cloud computing. Gillett sees cloud computingas revolutionary in the long term but over-hyped and misunderstood in theshort term, representing more of a gradual shift in our thinking aboutcomputer systems and not a sudden transformational change.[99][100]

Larry Ellison, CEO of Oracle Corporation has stated that cloud computinghas been defined as "everything that we already do" and that it will have noeffect except to "change the wording on some of our ads"[101][102]. OracleCorporation has since launched a cloud computing center and worldwidetour. Forrester Research Principal Analyst John Rymer dismisses Ellison'sremarks by stating that his "comments are complete nonsense and he knowsit".[103][104][105]

Richard Stallman said that cloud computing was simply a trap aimed atforcing more people to buy into locked, proprietary systems that would costthem more and more over time. "It's stupidity. It's worse than stupidity: it's amarketing hype campaign", he told The Guardian. "Somebody is saying thisis inevitable – and whenever you hear somebody saying that, it's very likelyto be a set of businesses campaigning to make it true." [106]

- Cloud computing is a general term for anything that involvesdelivering hosted services over the Internet. These services are broadlydivided into three categories: Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). The name cloudcomputing was inspired by the cloud symbol that's often used to represent

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the Internet in flowcharts and diagrams.

A cloud service has three distinct characteristics that differentiate it fromtraditional hosting. It is sold on demand, typically by the minute or thehour; it is elastic -- a user can have as much or as little of a service as theywant at any given time; and the service is fully managed by the provider (the consumer needs nothing but a personal computer and Internet access).Significant innovations in virtualization and distributed computing, as wellas improved access to high-speed Internet and a weak economy, haveaccelerated interest in cloud computing.

What are you interested in learning more

about?

a. Building a private cloud

 b. Using the cloud for development andtestingc. Security and the cloudd. Understanding cloud computing pricing

A cloud can be private or public. A public cloud sells services to anyone onthe Internet. (Currently, Amazon Web Services is the largest public cloud

 provider.) A private cloud is a proprietary network or a data center thatsupplies hosted services to a limited number of people. When a service

 provider uses public cloud resources to create their private cloud, the resultis called a virtual private cloud. Private or public, the goal of cloudcomputing is to provide easy, scalable access to computing resources andIT services.

Infrastructure-as-a-Service like Amazon Web Services provides virtualserver instances with unique IP addresses and blocks of storage on demand.Customers use the provider's application program interface (API) to start,stop, access and configure their virtual servers and storage. In theenterprise, cloud computing allows a company to pay for only as much

capacity as is needed, and bring more online as soon as required. Becausethis pay-for-what-you-use model resembles the way electricity, fuel andwater are consumed, it's 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 provider's infrastructure.Developers create applications on the provider's platform over the Internet.

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PaaS providers may use APIs, website portals or gateway software installedon the customer's computer. Force.com, (an outgrowth of Salesforce.com)and GoogleApps are examples of PaaS. Developers need to know thatcurrently, there are not standards for interoperability or data portability inthe cloud. Some providers will not allow software created by their customers to be moved off the provider's 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 anddatabase processing. Because the service provider hosts both the application and the data,the end user is free to use the service from anywhere

A hybrid cloud is a cloud computing environment in which an organization provides and manages some resources in-house and has others providedexternally. For example, an organization might use a public cloud service,such as Amazon Simple Storage Service (Amazon S3) for archived data butcontinue to maintain in-house storage for operational customer data. Ideally,the hybrid approach allows a business to take advantage of the scalabilityand cost-effectiveness that a public cloud computing environment offerswithout exposing mission-critical applications and data to third-partyvulnerabilities.

A public cloud is one based on the standard cloud computing model, inwhich a service provider makes resources, such as applications and storage,available to the general public over the Internet. Public cloud services may

 be free or offered on a pay-per-usage model.

The main benefits of using a public cloud service are:

•

Easy and inexpensive set-up because hardware, application and bandwidth costs are covered by the provider.• Scalability to meet needs.•  No wasted resources because you pay for what you use.

The term "public cloud" arose to differentiate between the standard modeland the private cloud, which is a proprietary network or data center that uses

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cloud computing technologies, such as virtualization. A private cloud ismanaged by the organization it serves. A third model, the hybrid cloud, ismaintained by both internal and external providers.

Examples of public clouds include Amazon Elastic Compute Cloud (EC2),IBM's Blue Cloud, Sun Cloud, Google AppEngine and Windows AzureServices Platform.

What is a private cloud?

Private cloud (also called internal cloud or corporate cloud) is a marketingterm for a proprietary computing architecture that provides hosted servicesto a limited number of people behind a firewall.

Advances in virtualization and distributed computing have allowedcorporate network and datacenter administrators to effectively becomeservice providers that meet the needs of their "customers" within thecorporation.

Marketing media that uses the words "private cloud" is designed to appeal toan organization that needs or wants more control over their data than theycan get by using a third-party hosted service such as Amazon's ElasticCompute Cloud (EC2) or Simple Storage Service (S3).

Let's say you're an executive at a large corporation. Your particular responsibilities include making sure that all of your employees have the righthardware and software they need to do their jobs. Buying computers for everyone isn't enough -- you also have to purchase software or software

licenses to give employees the tools they require. Whenever you have a newhire, you have to buy more software or make sure your current softwarelicense allows another user. It's so stressful that you find it difficult to go tosleep on your huge pile of money every night.

Soon, there may be an alternative for executives like you. Instead of installing a suite of software for each computer, you'd only have to load oneapplication. That application would allow workers to log into a Web-basedservice which hosts all the programs the user would need for his or her job.Remote machines owned by another company would run everything from e-

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mail to word processing to complex data analysis programs. It's called cloud

computing, and it could change the entire computer industry.

In a cloud computing system, there's a significant workload shift. Localcomputers no longer have to do all the heavy lifting when it comes torunning applications. The network of computers that make up the cloudhandles them instead. Hardware and software demands on the user's sidedecrease. The only thing the user's computer needs to be able to run is thecloud computing system's interface software, which can be as simple as aWeb browser, and the cloud's network takes care of the rest.

More Computing• Shared Computing• Utility Computing•

Grid Computing• ScienceChannel.com: Ubiquitous Computing

There's a good chance you've already used some form of cloud computing. If you have an e-mail account with a Web-based e-mail service like Hotmail,Yahoo! Mail or Gmail, then you've had some experience with cloudcomputing. Instead of running an e-mail program on your computer, you login to a Web e-mail account remotely. The software and storage for your account doesn't exist on your computer -- it's on the service's computer cloud

Cloud Computing Architecture

I Computed Lonely as a CloudAlthough cloud computing is an emerging field of computer science, the ideahas been around for a few years. It's called cloud computing because the dataand applications exist on a "cloud" of Web servers.

When talking about a cloud computing system, it's helpful to divide it intotwo sections: the front end and the back end. They connect to each other through a network , usually the Internet. The front end is the side thecomputer user, or client, sees. The back end is the "cloud" section of thesystem.

The front end includes the client's computer (or computer network) and theapplication required to access the cloud computing system. Not all cloudcomputing systems have the same user interface. Services like Web-based e-

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mail programs leverage existing Web browsers like Internet Explorer or Firefox. Other systems have unique applications that provide network accessto clients.

You've Been Virtually ServedMost of the time, servers don't run at full capacity. That means there's unused

 processing power going to waste. It's possible to fool a physical server intothinking it's actually multiple servers, each running with its own independentoperating system. The technique is called server virtualization. Bymaximizing the output of individual servers, server virtualization reduces theneed for more physical machines.

On the back end of the system are the various computers, servers and datastorage systems that create the "cloud" of computing services. In theory, a

cloud computing system could include practically any computer programyou can imagine, from data processing to video games. Usually, eachapplication will have its own dedicated server .

A central server administers the system, monitoring traffic and clientdemands to ensure everything runs smoothly. It follows a set of rules calledprotocols and uses a special kind of software called middleware.Middleware allows networked computers to communicate with each other.

Grids, Clouds and Utilities, Oh My!

Cloud computing is closely related to grid computing and utilitycomputing. In a grid computing system, networked computers are able toaccess and use the resources of every other computer on the network. Incloud computing systems, that usually only applies to the back end. Utilitycomputing is a business model where one company pays another companyfor access to computer applications or data storage.

If a cloud computing company has a lot of clients, there's likely to be a highdemand for a lot of storage space. Some companies require hundreds of 

digital storage devices. Cloud computing systems need at least twice thenumber of storage devices it requires to keep all its clients' informationstored. That's because these devices, like all computers, occasionally break down. A cloud computing system must make a copy of all its clients'information and store it on other devices. The copies enable the centralserver to access backup machines to retrieve data that otherwise would beunreachable. Making copies of data as a backup is called redundancy.

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What are some of the applications of cloud computing? Keep reading to findout.

Cloud Computing Applications

Who's Who in Cloud ComputingSome of the companies researching cloud computing are big names in thecomputer industry. Microsoft, IBM and Google are investing millions of dollars into research. Some people think Apple might investigate the

 possibility of producing interface hardware for cloud computing systems.

The applications of cloud computing are practically limitless. With the rightmiddleware, a cloud computing system could execute all the programs anormal computer could run. Potentially, everything from generic word

 processing software to customized computer programs designed for aspecific company could work on a cloud computing system.

Why would anyone want to rely on another computer system to run programs and store data? Here are just a few reasons:

• Clients would be able to access their applications and data fromanywhere at any time. They could access the cloud computing systemusing any computer linked to the Internet. Data wouldn't be confinedto a hard drive on one user's computer or even a corporation's internal

network.• It could bring hardware costs down. Cloud computing systems would

reduce the need for advanced hardware on the client side. Youwouldn't need to buy the fastest computer with the most memory,

 because the cloud system would take care of those needs for you.Instead, you could buy an inexpensive computer terminal. Theterminal could include a monitor , input devices like a keyboard andmouse and just enough processing power to run the middlewarenecessary to connect to the cloud system. You wouldn't need a largehard drive because you'd store all your information on a remotecomputer.

• Corporations that rely on computers have to make sure they have theright software in place to achieve goals. Cloud computing systemsgive these organizations company-wide access to computer applications. The companies don't have to buy a set of software or 

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software licenses for every employee. Instead, the company could paya metered fee to a cloud computing company.

• Servers and digital storage devices take up space. Some companiesrent physical space to store servers and databases because they don'thave it available on site. Cloud computing gives these companies theoption of storing data on someone else's hardware, removing the needfor physical space on the front end.

• Corporations might save money on IT support. Streamlined hardwarewould, in theory, have fewer problems than a network of heterogeneous machines and operating systems.

• If the cloud computing system's back end is a grid computing system,then the client could take advantage of the entire network's processing

 power. Often, scientists and researchers work with calculations socomplex that it would take years for individual computers to complete

them. On a grid computing system, the client could send thecalculation to the cloud for processing. The cloud system would tapinto the processing power of all available computers on the back end,significantly speeding up the calculation.

Cloud Computing Concerns

Private Eyes Are Watching YouThere are a few standard hacker tricks that could cause cloud computingcompanies major headaches. One of those is called key logging. A keylogging program records keystrokes. If a hacker manages successfully to loada key logging program on a victim's computer, he or she can study thekeystrokes to discover user names and passwords. Of course, if the user'scomputer is just a streamlined terminal, it might be impossible to install the

 program in the first place.

Perhaps the biggest concerns about cloud computing are security andprivacy. The idea of handing over important data to another companyworries some people. Corporate executives might hesitate to take advantageof a cloud computing system because they can't keep their company'sinformation under lock and key.

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The counterargument to this position is that the companies offering cloudcomputing services live and die by their reputations. It benefits thesecompanies to have reliable security measures in place. Otherwise, theservice would lose all its clients. It's in their interest to employ the mostadvanced techniques to protect their clients' data.

Privacy is another matter. If a client can log in from any location to accessdata and applications, it's possible the client's privacy could becompromised. Cloud computing companies will need to find ways to protectclient privacy. One way is to use authentication techniques such as user names and passwords. Another is to employ an authorization format -- eachuser can access only the data and applications relevant to his or her job.

Some questions regarding cloud computing are more philosophical. Does the

user or company subscribing to the cloud computing service own the data?Does the cloud computing system, which provides the actual storage space,own it? Is it possible for a cloud computing company to deny a client accessto that client's data? Several companies, law firms and universities aredebating these and other questions about the nature of cloud computing.

Same As It Ever WasCloud computing could turn home computers into simple terminal interfaces.In some ways, this is a step backward. Early computers included hardwireduser terminals. Each terminal had a computer monitor and keyboard, but they

only served as an interface to the main computer. There was no way to storeinformation locally on a terminal.

How will cloud computing affect other industries? There's a growingconcern in the IT industry about how cloud computing could impact the

 business of computer maintenance and repair. If companies switch to usingstreamlined computer systems, they'll have fewer IT needs. Some industryexperts believe that the need for IT jobs will migrate to the back end of thecloud computing system.

Another area of research in the computer science community is autonomic

computing. An autonomic computing system is self-managing, whichmeans the system monitors itself and takes measures to prevent or repair 

 problems. Currently, autonomic computing is mostly theoretical. But, if autonomic computing becomes a reality, it could eliminate the need for many IT maintenance jobs.