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Cloud computing logical diagram

Cloud computing is Internet-based computing, whereby shared resources, software and information are provided to computers and other devices on-demand, like a public utility.

It is a paradigm shift following the shift from mainframe to client-server that preceded it. Details are abstracted from the users who no longer have need of, expertise in, or control over the technology infrastructure "in the cloud" that supports them.[1] Cloud computing describes an new supplement, consumption and delivery model for IT services based on the Internet, and it typically involves the provision of dynamically scalable and often virtualized resources as a service over the Internet.[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 cloud drawing used in the past to represent the telephone network [5], and later to depict the Internet in computer network diagrams as an abstraction of the underlying infrastructure it represents.[6] Typical cloud computing providers deliver common business applications online which are accessed from a web browser, while the software and data are stored on servers.

A technical definition is "a computing capability that provides an abstraction between the computing resource and its underlying technical architecture (e.g., servers, storage, networks), enabling convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction."[7] This definition states that clouds have five essential characteristics: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.[7]

The majority of cloud computing infrastructure, as of 2009, consists of reliable services delivered through data centers and built on servers. Clouds often appear as single points of access for all consumers' computing needs. Commercial offerings are generally expected to meet quality of service (QoS) requirements of customers and typically offer SLAs.[8]




Cloud computing derives characteristics from, but should not be confused with:

  1. Autonomic computing — "computer systems capable of self-management".[9]
  2. Client-server – Client-server computing refers broadly to any distributed application that distinguishes between service providers (servers) and service requesters (clients).[10]
  3. Grid computing — "a form of distributed computing and parallel computing, whereby a 'super and virtual computer' is composed of a cluster of networked, loosely coupled computers acting in concert to perform very large tasks"
  4. Mainframe — powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.[11]
  5. Utility computing — the "packaging of computing resources, such as computation and storage, as a metered service similar to a traditional public utility, such as electricity";[12]


In general, cloud computing customers do not own the physical infrastructure, instead avoiding capital expenditure by renting usage from a third-party provider. They consume resources as a service and pay only for resources that they use. Many cloud-computing offerings employ the utility computing 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 multiple tenants 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 overall computer usage rises dramatically, as customers do not have to engineer for peak load limits.[13] In addition, "increased high-speed bandwidth" makes it possible to receive the same response times from centralized infrastructure at other sites[14].


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, like electricity) 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 terminate the contract at any time (thereby avoiding return on investment risk and uncertainty), and the services are often covered by service level agreements (SLAs) with financial penalties.[15][16]

According to Nicholas Carr, the strategic importance of information technology is diminishing as it becomes standardized and less expensive. He argues that the cloud computing paradigm shift is similar to the displacement of electricity generators by electricity grids early in the 20th century.[17]

Although companies might be able to save on upfront capital expenditures, they might not save much and might actually pay more for operating expenses. In situations where the capital expense would be relatively small, or where the organization has more flexibility in their capital budget than their operating budget, the cloud model might not make great fiscal sense. Other factors impacting the scale of any potential cost savings include the efficiency of a company’s data center as compared to the cloud vendor’s, the company's existing operating costs, the level of adoption of cloud computing, and the type of functionality being hosted in the cloud.[18][19]


Cloud computing sample architecture

Cloud architecture,[20] 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.[21] This closely resembles the Unix philosophy of having multiple programs each doing one thing well and working together over universal interfaces. Complexity is controlled and the resulting systems are more manageable than their monolithic counterparts.


The underlying concept of cloud computing dates back to 1960, when John McCarthy opined that "computation may someday be organized as a public utility"; indeed it shares characteristics with service bureaus that date back to the 1960s. The actual term "cloud" borrows from telephony in that telecommunications companies, who until the 1990s primarily offered dedicated point-to-point data circuits, began offering Virtual Private Network (VPN) services with comparable quality of service but at a much lower cost. By switching traffic to balance utilization as they saw fit they were able to utilise their overall network 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 to cover servers as well as the network infrastructure.[22]

Amazon played a key role in the development of cloud computing by modernizing their data centers after the dot-com bubble, which, like most computer networks, were using as little as 10% of their capacity at any one time just to leave room for occasional spikes. Having found that the new cloud architecture resulted in significant internal efficiency improvements whereby small, fast-moving "two-pizza teams" could add new features faster and easier, Amazon started providing access to their systems through Amazon Web Services on a utility computing basis in 2005.[23]

In 2007, Google, IBM, and a number of universities embarked on a large scale cloud computing research project.[24] By mid-2008, Gartner saw an opportunity for cloud computing "to shape the relationship among consumers of IT services, those who use IT services and those who sell them",[25] and observed that "[o]rganisations are switching from company-owned hardware and software assets to per-use service-based models" so that the "projected shift to cloud computing ... will result in dramatic growth in IT products in some areas and in significant reductions in other areas."[26]

Key features

  • Agility improves with users' ability to rapidly and inexpensively re-provision technological infrastructure resources.[27]
  • Cost is claimed to be greatly reduced and capital expenditure is converted to operational expenditure[28]. 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 infrequent intensive 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).[29]
  • Device and location independence[30] enable users to access systems using a web browser regardless of their location or what device they are using (e.g., PC, mobile). As infrastructure is off-site (typically provided by a third-party) and accessed via the Internet, users can connect from anywhere.[29]
  • Multi-tenancy enables sharing of resources and costs across a large pool of users thus allowing for:
    • Centralization of infrastructure in locations with lower costs (such as real estate, electricity, etc.)
    • Peak-load capacity increases (users need not engineer for highest possible load-levels)
    • Utilization and efficiency improvements for systems that are often only 10–20% utilized.[23]
  • Reliability improves through the use of multiple redundant sites, which makes cloud computing suitable for business continuity and disaster recovery.[31] Nonetheless, many major cloud computing services have suffered outages, and IT and business managers can at times do little when they are affected.[32][33]
  • Scalability via dynamic ("on-demand") provisioning of resources on a fine-grained, self-service basis near real-time, without users having to engineer for peak loads. Performance is monitored, and consistent and loosely-coupled architectures are constructed using web services as the system interface.[29] 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.[34]
  • Security could improve due to centralization of data[35], increased security-focused resources, etc., but concerns can persist about loss of control over certain sensitive data, and the lack of security for stored kernels[36]. Security is often as good as or better than under traditional systems, in part because providers are able to devote resources to solving security issues that many customers cannot afford.[37] Providers typically log accesses, but accessing the audit logs themselves can be difficult or impossible. Furthermore, the complexity of security is greatly increased when data is distributed over 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 are easier to support and to improve since the changes reach the clients instantly.
  • Metering cloud computing resources usage should be measurable and should be metered per client and application on daily, weekly, monthly, and annual basis. This will enable clients on choosing the vendor cloud on cost and reliability (QoS).


Cloud Computing Stack.svg


See also Category: Cloud clients

A cloud client consists of computer hardware and/or computer software that relies on cloud computing for application delivery, or that is specifically designed 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.[38][39][40][41][42]


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 the application on the customer's own computers and simplifying maintenance and support. Key characteristics include:[43]

  • Network-based access to, and management of, commercially available (i.e., not custom) software
  • Activities that are managed from central locations rather than at each customer's site, enabling customers to access applications remotely via the Web
  • 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 management characteristics
  • Centralized feature updating, which obviates the need for downloadable patches and upgrades.


See also Category: Cloud platforms

Cloud platform services or "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.[44][45]


See also Category: Cloud infrastructure

Cloud infrastructure services or "Infrastructure as a Service (IaaS)" delivers computer infrastructure, typically a platform virtualization environment, as a service. Rather than purchasing servers, software, data center space or network equipment, clients instead buy those resources as a fully outsourced service. The service is typically billed on a utility computing basis and amount of resources consumed (and therefore the cost) will typically reflect the level of activity. It is an evolution of virtual private server offerings.[46]


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.[38][47][48][49]

Deployment models

Cloud computing types

Public cloud

Public cloud or external cloud describes cloud computing in the traditional mainstream sense, whereby resources are dynamically provisioned on a fine-grained, self-service basis over the Internet, via web applications/web services, from an off-site third-party provider who shares resources and bills on a fine-grained utility computing basis.[29]

Community cloud

A community cloud may be established where several organizations have similar requirements and seek to share infrastructure so as to realize some of the benefits of cloud computing. With the costs spread over fewer users than a 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".[50]

Hybrid cloud

A hybrid cloud environment consisting of multiple internal and/or external providers[51] "will be typical for most enterprises".[52] By integrating multiple cloud services users may be able to ease the transition to public cloud services while avoiding issues such as PCI compliance.[53]

Another perspective on deploying a web application in the cloud is using Hybrid Web Hosting, where the hosting infrastructure is a mix between Cloud Hosting for the web server, and Managed dedicated server for the database server.[54]

Private cloud

Private cloud and internal cloud are neologisms that some vendors have recently used to describe offerings that emulate cloud computing on private networks. These (typically virtualisation automation) products claim to "deliver some benefits of cloud computing without the pitfalls", capitalising on data security, corporate governance, and reliability concerns. 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[52], essentially "[lacking] the economic model that makes cloud computing such an intriguing concept".[55][56]

The term has also been used in the logical rather than physical sense, for example in reference to platform as a service offerings[57], though such offerings including Microsoft's Azure Services Platform are not available for on-premises deployment.[58]



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 data stored between the user and the host company. Instances such as the secret NSA program, working with AT&T, Verizon and BellSouth, which recorded over 10 million phone calls between American citizens, causes uncertainty among privacy advocates, and the greater powers it gives to telecommunication companies to monitor user activity.[59] While there have been efforts (such as US-EU Safe Harbor) to "harmonise" the legal environment, providers such as Amazon still cater to major markets (typically the United States and the European Union) by deploying local infrastructure and allowing customers to select "availability zones."[60]


In order to obtain compliance with regulations including FISMA, HIPAA and SOX in the US, the Data Protection Directive in the EU and 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 are able to "manage and meet additional government policy requirements beyond FISMA"[61][62] and Rackspace Cloud are able to claim PCI compliance.[63]

Many providers also obtain SAS 70 Type II certification (e.g. Amazon[64], Google[65] and Microsoft[66]), but this has been criticised on 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.[67] Providers typically make this information available on request, under non-disclosure agreement.[68]


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" the company received in July 2008 was cancelled in August, resulting in a formal rejection of the trademark application less than a week later.

Open source

Open standards are critical to the growth of cloud computing, and open source software has provided the foundation for many cloud computing implementations.[69] 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.[70]

Open standards

See also Category: Cloud standards

Most cloud providers expose APIs which are typically well-documented (often under a Creative Commons license[71]) however also unique to their implementation and thus not interoperable. Some vendors have adopted others' APIs[72] and there are a number of open standards under development, including the OGF's Open Cloud Computing Interface.


The relative security of cloud computing services is a contentious issue which may be delaying its adoption.[73] Some argue that customer data is more secure when managed internally, while others argue that cloud providers have a strong incentive to maintain trust and as such employ a higher level of security.[74]


Although cloud computing is often assumed to be a form of "green computing", there is as of yet no published study to substantiate this assumption. [75]


A number of universities, vendors and government organizations are investing in research around the topic of cloud computing.[76] Academic institutions 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, North Carolina State, Purdue, University of California, University of Washington, University of Virginia, University of Utah, University of Minnesota, among others.[77]

Joint government, academic and vendor collaborative research projects include the IBM/Google Academic Cloud Computing Initiative (ACCI). In October 2007 IBM and Google announced the multi- university project designed to enhance students’ technical knowledge to address the challenges of cloud computing.[78] In April 2009, the National Science Foundation joined the ACCI and awarded approximately $5 million in grants to 14 academic institutions.[79]

In July 2008, HP, Intel Corporation and Yahoo! announced the creation of a global, multi-data center, open source test bed, called Open Cirrus[80], designed to encourage research into all aspects of cloud computing, service and datacenter management.[81] Open Cirrus partners include the NSF, the University of Illinois (UIUC), Karlsruhe Institute of Technology, the Infocomm Development Authority (IDA) of Singapore, the Electronics and Telecommunications Research Institute (ETRI), the Malaysian Institute for Microelectronic Systems(MIMOS), and the Institute for System Programming at the Russian Academy of Sciences (ISPRAS).[82]

The Enabling Grids for E-sciencE (EGEE) project provides the world's largest production grid infrastructure for applications for use by more than 10,000 researchers from 50 countries, according to the European Union EGEE Web site.[83]

The IEEE Technical Committee on Services Computing [84] in IEEE Computer Society sponsors the IEEE International Conference on Cloud Computing (CLOUD)[85]. CLOUD 2010 will be held on July 5-10, 2010 in Miami, Florida.

Criticism of the term

Notable industry critics of the term include Oracle Corporation CEO Larry Ellison and Forrester Research VP Frank Gillett. Larry Ellison has stated that cloud computing has been defined as "everything that we currently do" and that it will have no effect except to "change the wording on some of our ads"[86][87]. Frank Gillett expresses similar criticism [88][89].

Oracle Corporation is now launching a cloud computing tour [90].

In opposition to Larry Ellison, Forrester Research Principal Analyst John Rymer dismisses his remarks by stating that Ellison's cloud "comments are complete nonsense and he knows it" [91].

Richard Stallman, founder of the Free Software Foundation and creator of the computer operating system GNU, said that cloud computing was simply a trap aimed at forcing more people to buy into locked, proprietary systems that would cost them more and more over time. "It's stupidity. It's worse than stupidity: it's a marketing hype campaign," he told The Guardian. "Somebody is saying this is inevitable – and whenever you hear somebody saying that, it's very likely to be a set of businesses campaigning to make it true." "The interesting thing about cloud computing is that we've redefined cloud computing to include everything that we already do," he said. "[92]


  1. ^ Distinguishing Cloud Computing from Utility Computing
  2. ^ Gartner Says Cloud Computing Will Be As Influential As E-business
  3. ^ Gruman, Galen (2008-04-07). "What cloud computing really means". InfoWorld. Retrieved 2009-06-02. 
  4. ^ "Cloud Computing: Clash of the clouds". The Economist. 2009-10-15. Retrieved 2009-11-03. 
  5. ^
  6. ^ The Internet Cloud
  7. ^ a b Cloud Computing Definition, National Insitute of Standards and Technology, Version 15
  8. ^ Buyya, Rajkumar; Chee Shin Yeo, Srikumar Venugopal (PDF). Market-Oriented Cloud Computing: Vision, Hype, and Reality for Delivering IT Services as Computing Utilities. Department of Computer Science and Software Engineering, The University of Melbourne, Australia. pp. 9. Retrieved 2008-07-31. 
  9. ^ What's In A Name? Utility vs. Cloud vs Grid
  10. ^ "Distributed Application Architecture". Sun Microsystem. Retrieved 2009-06-16. 
  11. ^ Sun CTO: Cloud computing is like the mainframe
  12. ^ "It's probable that you’ve misunderstood 'Cloud Computing' until now". TechPluto. 
  13. ^ Cloud Computing: The Evolution of Software-as-a-Service
  14. ^ Needs Reference
  15. ^ Forrester's Advice to CFOs: Embrace Cloud Computing to Cut Costs
  16. ^ Five cloud computing questions
  17. ^ Nicholas Carr on 'The Big Switch' to cloud computing
  18. ^ 1 Midsize Organization Busts 5 Cloud Computing Myths
  19. ^ Cloud Computing Savings - Real or Imaginary?
  20. ^ Building GrepTheWeb in the Cloud, Part 1: Cloud Architectures
  21. ^ Cloud Maturity is Accelerating: More Than Just Reaction To The Hype?
  22. ^ July, 1993 meeting report from the IP over ATM working group of the IETF
  23. ^ a b Jeff Bezos' Risky Bet.
  24. ^ Google and I.B.M. Join in ‘Cloud Computing’ Research
  25. ^ Keep an eye on cloud computing, Amy Schurr, Network World, 2008-07-08, citing the Gartner report, “Cloud Computing Confusion Leads to Opportunity”. Retrieved 2009-09-11.
  26. ^ Gartner Says Worldwide IT Spending On Pace to Surpass $3.4 Trillion in 2008, Gartner, 2008-08-18. Retrieved 2009-09-11.
  27. ^ Infrastructure Agility: Cloud Computing as a Best Practice
  28. ^ Recession Is Good For Cloud Computing – Microsoft Agrees
  29. ^ a b c d Defining “Cloud Services” and “Cloud Computing”
  30. ^ The new geek chic: Data centers
  31. ^ Cloud Computing: Small Companies Take Flight
  32. ^ Google Apps Admins Jittery About Gmail, Hopeful About Future
  33. ^ New Resource, Born of a Cloud Feud
  34. ^ Scaling Storage and Analysis of Data Using Distributed Data Grids
  35. ^ Exari: Death By Laptop
  36. ^ Encrypted Storage and Key Management for the cloud
  37. ^ Cloud computing security forecast: Clear skies
  38. ^ a b Nimbus Cloud Guide
  39. ^ Microsoft’s cloud operating system, Windows Azure, to go live in January
  40. ^ Google Reveals Nexus One 'Super Phone'
  41. ^ What Makes a Cloud Computer?
  42. ^ The Cloud's Chrome Lining
  43. ^ 2005 Software as a Service Taxonomy and Research Guide
  44. ^ Google angles for business users with 'platform as a service'
  45. ^ The Emerging Cloud Service Architecture
  46. ^ EMC buys Pi and forms a cloud computing group
  47. ^ Intel puts cloud on single megachip
  48. ^ Cisco unveils cloud computing platform for service providers
  49. ^ Microsoft Plans ‘Cloud’ Operating System
  50. ^ Google's "Gov Cloud" Wins $7.2 Million Los Angeles Contract
  51. ^ IBM Embraces Juniper For Its Smart 'Hybrid Cloud', Disses Cisco (IBM)
  52. ^ a b Private Clouds Take Shape
  53. ^ Forecast for 2010: The Rise of Hybrid Clouds
  54. ^ Hybrid Hosting: Using the Best of Managed and Cloud
  55. ^ Just don't call them private clouds
  56. ^ There's No Such Thing As A Private Cloud
  57. ^ Google opens private cloud to coders
  58. ^ Microsoft Nixes Private Azure Clouds
  59. ^ NSA has massive database of Americans' phone calls
  60. ^ Feature Guide: Amazon EC2 Availability Zones
  61. ^ FISMA compliance for federal cloud computing on the horizon in 2010
  62. ^ Google Apps and Government
  63. ^ Cloud Hosting is Secure for Take-off: Mosso Enables The Spreadsheet Store, an Online Merchant, to become PCI Compliant
  64. ^ AWS Completes SAS70 Type II Audit
  65. ^ SAS 70 Type II for Google Apps
  66. ^ Securing Microsoft’s Cloud Infrastructure
  67. ^ Amazon gets SAS 70 Type II audit stamp, but analysts not satisfied
  68. ^ Assessing Cloud Computing Agreements and Controls
  69. ^ Open source fuels growth of cloud computing, software-as-a-service
  70. ^ AGPL: Open Source Licensing in a Networked Age
  71. ^ GoGrid Moves API Specification to Creative Commons
  72. ^ Eucalyptus Completes Amazon Web Services Specs with Latest Release
  73. ^ Are security issues delaying adoption of cloud computing?
  74. ^ Security of virtualization, cloud computing divides IT and security pros
  75. ^ James Urquhart (January 7, 2010). "Cloud computing's green paradox". CNET News. Retrieved March 12, 2010. "...there is some significant evidence that the cloud is encouraging more compute consumption" 
  76. ^ Cloud Net Directory. Retrieved 2010-03-01.
  77. ^ National Science Foundation Press Release 09-082. ”National Science Foundation Awards Millions to Fourteen Universities for Cloud Computing Research.”
  78. ^ IBM press release from Retrieved 2010-03-02.
  79. ^ National Science Foundation press release. Retrieved 2010-03-01.
  80. ^ HP News Release
  81. ^ HP News Release
  82. ^ Open Cirrus: the Open Cloud Computing Research Testbed
  83. ^ EGEE Web site. Retrieved 2010-03002.
  84. ^ IEEE Technical Committee on Services Computing
  85. ^ IEEE International Conference on Cloud Computing (CLOUD)
  86. ^ Larry Ellison - What The Hell Is Cloud Computing?
  87. ^ Oracle's Ellison nails cloud computing
  88. ^ Cloud Computing is Hyped and Overblown, Forrester's
  89. ^ Cloud Computing is Hyped and Overblown, Forrester's Frank Gillett.....Big Tech Companies Have "Cloud Envy"
  90. ^ Oracle launches worldwide cloud-computing tour
  91. ^ Oracle desperately seeking cloud cred
  92. ^ Cloud computing is a trap, warns GNU founder Richard Stallman The Guardian, Monday 29 September 2008 14.11 BST


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