A private cloud is a particular model of cloud computing that involves a distinct and secure cloud based environment in which only the specified client can operate. As with other cloud models, private clouds will provide computing power as a service within a virtualized environment using an underlying pool of physical computing resource. However, under the private cloud model, the cloud (the pool of resource) is only accessible by a single organization providing that organization with greater control and privacy.

The technical mechanisms used to provide the different services which can be classed as being private cloud services can vary considerably and so it is hard to define what constitutes a private cloud from a technical aspect. Instead such services are usually categorized by the features that they offer to their client. Traits that characterize private clouds include the ring fencing of a cloud for the sole use of one organization and higher levels of network security. They can be defined in contrast to a public cloud which has multiple clients accessing virtualized services which all draw their resource from the same pool of servers across public networks. Private cloud services draw their resource from a distinct pool of physical computers but these may be hosted internally or externally and may be accessed across private leased lines or secure encrypted connections via public networks.

The additional security offered by the ring fenced cloud model is ideal for any organization, including enterprise, that needs to store and process private data or carry out sensitive tasks. For example, a private cloud service could be utilized by a financial company that is required by regulation to store sensitive data internally and who will still want to benefit from some of the advantages of cloud computing within their business infrastructure, such as on demand resource allocation.

The private cloud model is closer to the more traditional model of individual local access networks (LANs) used in the past by enterprise but with the added advantages of virtualization. The features and benefits of private clouds therefore are:

• Higher security and privacy; public clouds services can implement a certain level of security but private clouds - using techniques such as distinct pools of resources with access restricted to connections made from behind one organization's firewall, dedicated leased lines and/or on-site internal hosting - can ensure that operations are kept out of the reach of prying eyes

• More control; as a private cloud is only accessible by a single organization, that organization will have the ability to configure and manage it in line with their needs to achieve a tailored network solution. However, this level of control removes some of the economies of scale generated in public clouds by having centralized management of the hardware

• Cost and energy efficiency; implementing a private cloud model can improve the allocation of resources within an organization by ensuring that the availability of resources to individual departments/business functions can directly and flexibly respond to their demand. Therefore, although they are not as cost effective as a public cloud services due to smaller economies of scale and increased management costs, they do make more efficient use of the computing resource than traditional LANs as they minimize the investment into unused capacity. Not only does this provide a cost saving but it can reduce an organization's carbon footprint too

• Improved reliability; even where resources (servers, networks etc.) are hosted internally, the creation of virtualized operating environments means that the network is more resilient to individual failures across the physical infrastructure. Virtual partitions can, for example, pull their resource from the remaining unaffected servers. In addition, where the cloud is hosted with a third party, the organization can still benefit from the physical security afforded to infrastructure hosted within data centers

• Cloud bursting; some providers may offer the opportunity to employ cloud bursting, within a private cloud offering, in the event of spikes in demand. This service allows the provider to switch certain non-sensitive functions to a public cloud to free up more space in the private cloud for the sensitive functions that require it. Private clouds can even be integrated with public cloud services to form hybrid clouds where non-sensitive functions are always allocated to the public cloud to maximize the efficiencies on offer

The most recognizable model of cloud computing to many consumers is the public cloud model, under which cloud services are provided in a virtualized environment, constructed using pooled shared physical resources, and accessible over a public network such as the internet. To some extent they can be defined in contrast to private clouds which ring-fence the pool of underlying computing resources, creating a distinct cloud platform to which only a single organization has access. Public clouds, however, provide services to multiple clients using the same shared infrastructure.

The technical mechanisms used to provide the different services which can be classed as being private cloud services can vary considerably and so it is hard to define what constitutes a private cloud from a technical aspect. Instead such services are usually categorized by the features that they offer to their client. Traits that characterize private clouds include the ring fencing of a cloud for the sole use of one organization and higher levels of network security. They can be defined in contrast to a public cloud which has multiple clients accessing virtualized services which all draw their resource from the same pool of servers across public networks. Private cloud services draw their resource from a distinct pool of physical computers but these may be hosted internally or externally and may be accessed across private leased lines or secure encrypted connections via public networks.

The most salient examples of cloud computing tend to fall into the public cloud model because they are, by definition, publicly available. Software as a Service (SaaS) offerings such as cloud storage and online office applications are perhaps the most familiar, but widely available Infrastructure as a Service (IaaS) and Platform as a Service (PaaS) offerings, including cloud based web hosting and development environments, can follow the model as well (although all can also exist within private clouds). Public clouds are used extensively in offerings for private individuals who are less likely to need the level of infrastructure and security offered by private clouds. However, enterprise can still utilise public clouds to make their operations significantly more efficient, for example, with the storage of non-sensitive content, online document collaboration and webmail.

The public model offers the following features and benefits:

• Ultimate scalability; cloud resources are available on demand from the public clouds’ vast pools of resource so that the applications that run on them can respond seamlessly to fluctuations in activity.

• Cost effective; public clouds bring together greater levels of resource and so can benefit from the largest economies of scale. The centralized operation and management of the underlying resources is shared across all of the subsequent cloud services whilst components, such as servers, require less bespoke configuration. Some mass market propositions can even be free to the client, relying on advertising for their revenue.

• Utility style costing;public cloud services often employ a pay-as-you-go charging model whereby the consumer will be able to access the resource they need, when they need it, and then only pay for what they use; therefore avoiding wasted capacity.

• Reliability; the sheer number of servers and networks involved in creating a public cloud and the redundancy configurations mean that should one physical component fail, the cloud service would still run unaffected on the remaining components. In some cases, where clouds draw resource from multiple data centers, an entire data centre could go offline and individual cloud services would suffer no ill effect. There is, in other words, no single point of failure which would make a public cloud service vulnerable.

• Flexibility;there are a myriad of IaaS, PaaS and SaaS services available on the market which follow the public cloud model and that are ready to be accessed as a service from any internet enabled device. These services can fulfill most computing requirements and can deliver their benefits to private and enterprise clients alike. Businesses can even integrate their public cloud services with private clouds, where they need to perform sensitive business functions, to create hybrid clouds.

• Location independence;the availability of public cloud services through an internet connection ensures that the services are available wherever the client is located. This provides invaluable opportunities to enterprise such as remote access to IT infrastructure (in case of emergencies etc) or online document collaboration from multiple locations..

A hybrid cloud is an integrated cloud service utilizing both private and public clouds to perform distinct functions within the same organization. All cloud computing services should offer certain efficiencies to differing degrees but public cloud services are likely to be more cost efficient and scalable than private clouds. Therefore, an organization can maximize their efficiencies by employing public cloud services for all non-sensitive operations, only relying on a private cloud where they require it and ensuring that all of their platforms are seamlessly integrated.

Hybrid cloud models can be implemented in a number of ways:

• Separate cloud providers team up to provide both private and public services as an integrated service.

• Individual cloud providers offer a complete hybrid package.

• Organizations who manage their private clouds themselves sign up to a public cloud service which they then integrate into their infrastructure.

In practice, an enterprise could implement hybrid cloud hosting to host their e-commerce website within a private cloud, where it is secure and scalable, but their brochure site in a public cloud, where it is more cost effective (and security is less of a concern). Alternatively, an Infrastructure as a Service (IaaS) offering, for example, could follow the hybrid cloud model and provide a financial business with storage for client data within a private cloud, but then allow collaboration on project planning documents in the public cloud - where they can be accessed by multiple users from any convenient location.

A hybrid cloud configuration, such as hybrid hosting, can offer its users the following features:

• Scalability; whilst private clouds do offer a certain level of scalability depending on their configurations (whether they are hosted internally or externally for example), public cloud services will offer scalability with fewer boundaries because resource is pulled from the larger cloud infrastructure. By moving as many non-sensitive functions as possible to the public cloud it allows an organization to benefit from public cloud scalability whilst reducing the demands on a private cloud..

• Cost efficiencies; again public clouds are likely to offer more significant economies of scale (such as centralized management), and so greater cost efficiencies, than private clouds. Hybrid clouds therefore allow organizations to access these savings for as many business functions as possible whilst still keeping sensitive operations secure.

• Securitythe private cloud element of the hybrid cloud model not only provides the security where it is needed for sensitive operations but can also satisfy regulatory requirements for data handling and storage where it is applicable.

• Flexiblity; the availability of both secure resource and scalable cost effective public resource can provide organizations with more opportunities to explore different operational avenues.

In some respects cloud servers work in the same way as physical servers but the functions they provide can be very different. When opting for cloud hosting, clients are renting virtual server space rather than renting or purchasing physical servers. They are often paid for by the hour depending on the capacity required at any particular time.

Traditionally there are two main options for hosting: shared hosting and dedicated hosting. Shared hosting is the cheaper option whereby servers are shared between the hosting provider’s clients. One client’s website will be hosted on the same server as websites belonging to other clients. This has several disadvantages including the fact that the setup is inflexible and cannot cope with a large amount of traffic. Dedicated hosting is a much more advanced form of hosting, whereby clients purchase whole physical servers. This means that the entire server is dedicated to them with no other clients sharing it. In some instances the client may utilise multiple servers which are all dedicated to their use. Dedicated servers allow for full control over hosting. The downside is that the required capacity needs to be predicted, with enough resource and processing power to cope with expected traffic levels. If this is underestimated then it can lead to a lack of necessary resource during busy periods, while overestimating it will mean paying for unnecessary capacity.

With cloud hosting clients get the best of both worlds. Resource can be scaled up or scaled down accordingly, making it more flexible and, therefore, more cost-effective. When there is more demand placed on the servers, capacity can be automatically increased to match that demand without this needing to be paid for on a permanent basis. This is akin to a heating bill; you access what you need, when you need it, and then only pay for what you’ve used afterwards.

Unlike dedicated servers, cloud servers can be run on a hypervisor. The role of a hypervisor is to control the capacity of operating systems so it is allocated where needed. With cloud hosting there are multiple cloud servers which are available to each particular client. This allows computing resource to be dedicated to a particular client if and when it is necessary. Where there is a spike in traffic, additional capacity will be temporarily accessed by a website, for example, until it is no longer required. Cloud servers also offer more redundancy. If one server fails, others will take its place.

Below are the key benefits of cloud servers:

• Flexibility and scalability; extra resource can be accessed as and when required.

• Cost-effectiveness;whilst being available when needed, clients only pay for what they are using at a particular time.

• Ease of setupCloud servers do not require much initial setup.

• Realiablity;due to the number of available servers, if there are problems with some, the resource will be shifted so that clients are unaffected.

Infrastructure as a Service (IaaS) is one of the three fundamental service models of cloud computing alongside Platform as a Service (PaaS) and Software as a Service (SaaS). As with all cloud computing services it provides access to computing resource in a virtualized environment, “the Cloud”, across a public connection, usually the internet. In the case of IaaS the computing resource provided is specifically that of virtualized hardware, in other words, computing infrastructure.

The definition includes such offerings as virtual server space, network connections, bandwidth, IP addresses and load balancers. Physically, the pool of hardware resource is pulled from a multitude of servers and networks usually distributed across numerous data centers, all of which the cloud provider is responsible for maintaining. The client, on the other hand, is given access to the virtualized components in order to build their own IT platforms.

In common with the other two forms of cloud hosting, IaaS can be utilized by enterprise customers to create cost effective and easily scalable IT solutions where the complexities and expenses of managing the underlying hardware are outsourced to the cloud provider. If the scale of a business customer’s operations fluctuate, or they are looking to expand, they can tap into the cloud resource as and when they need it rather than purchase, install and integrate hardware themselves.

A typical Infrastructure as a Service offering can deliver the following features and benefits:

• Scalability;resource is available as and when the client needs it and, therefore, there are no delays in expanding capacity or the wastage of unused capacity.

• No investment in hardware;the underlying physical hardware that supports an IaaS service is set up and maintained by the cloud provider, saving the time and cost of doing so on the client side.

• Utility style costingthe service can be accessed on demand and the client only pays for the resource that they actually use.

• Location independence;the service can usually be accessed from any location as long as there is an internet connection and the security protocol of the cloud allows it.

• Physical security of data centre locations;services available through a public cloud, or private clouds hosted externally with the cloud provider, benefit from the physical security afforded to the servers which are hosted within a data centre.

• No single point of failure;if one server or network switch, for example, were to fail, the broader service would be unaffected due to the remaining multitude of hardware resources and redundancy configurations. For many services if one entire data center were to go offline, never mind one server, the IaaS service could still run successfully.

Platform as a Service, often simply referred to as PaaS, is a category of cloud computing that provides a platform and environment to allow developers to build applications and services over the internet. PaaS services are hosted in the cloud and accessed by users simply via their web browser.

Platform as a Service allows users to create software applications using tools supplied by the provider. PaaS services can consist of preconfigured features that customers can subscribe to; they can choose to include the features that meet their requirements while discarding those that do not. Consequently, packages can vary from offering simple point-and-click frameworks where no client side hosting expertise is required to supplying the infrastructure options for advanced development.

The infrastructure and applications are managed for customers and support is available. Services are constantly updated, with existing features upgraded and additional features added. PaaS providers can assist developers from the conception of their original ideas to the creation of applications, and through to testing and deployment. This is all achieved in a managed mechanism.

The infrastructure and applications are managed for customers and support is available. Services are constantly updated, with existing features upgraded and additional features added. PaaS providers can assist developers from the conception of their original ideas to the creation of applications, and through to testing and deployment. This is all achieved in a managed mechanism.

Below are some of the features that can be included with a PaaS offering:

• Operating system

• Database management system

• Server Software

• Support

• Storage

• Network access

• Tools for design and development

• Hosting

Software developers, web developers and businesses can benefit from PaaS. Whether building an application which they are planning to offer over the internet or software to be sold out of the box, software developers may take advantage of a PaaS solution. For example, web developers can use individual PaaS environments at every stage of the process to develop, test and ultimately host their websites. However, businesses that are developing their own internal software can also utilise Platform as a Service, particularly to create distinct ring-fenced development and testing environments.

In summary, a PaaS offering supplies an operating environment for developing applications. In other words, it provides the architecture as well as the overall infrastructure to support application development. This includes networking, storage, software support and management services. It is therefore ideal for the development of new applications that are intended for the web as well as mobile devices and PCs.

SaaS, or Software as a Service, describes any cloud service where consumers are able to access software applications over the internet. The applications are hosted in “the cloud” and can be used for a wide range of tasks for both individuals and organizations. Google, Twitter, Facebook and Flickr are all examples of SaaS, with users able to access the services via any internet enabled device. Enterprise users are able to use applications for a range of needs, including accounting and invoicing, tracking sales, planning, performance monitoring and communications (including webmail and instant messaging).

SaaS is often referred to as software-on-demand and utilizing it is akin to renting software rather than buying it. With traditional software applications you would purchase the software upfront as a package and then install it onto your computer. The software’s license may also limit the number of users and/or devices where the software can be deployed. Software as a Service users, however, subscribe to the software rather than purchase it, usually on a monthly basis. Applications are purchased and used online with files saved in the cloud rather than on individual computers.

There are a number of reasons why SaaS is beneficial to organizations and personal users alike:

• No additional hardware cost;the processing power required to run the applications is supplied by the cloud provider.

• No initial setup costs;; applications are ready to use once the user subscribes.

• Pay for what you useif a piece of software is only needed for a limited period then it is only paid for over that period and subscriptions can usually be halted at any time.

• Usage is scalable;if a user decides they need more storage or additional services, for example, then they can access these on demand without needing to install new software or hardware.

• Updates are automated;whenever there is an update it is available online to existing customers, often free of charge. No new software will be required as it often is with other types of applications and the updates will usually be deployed automatically by the cloud provider.

• Cross device compatibility;SaaS applications can be accessed via any internet enabled device, which makes it ideal for those who use a number of different devices, such as internet enabled phones and tablets, and those who don’t always use the same computer.

• Accessible from any location; rather than being restricted to installations on individual computers, an application can be accessed from anywhere with an internet enabled device.

• Applications can be customized and white labelled; with some software, customization is available meaning it can be altered to suit the needs and branding of a particular customer.

Office software is the best example of businesses utilizing SaaS. Tasks related to accounting, invoicing, sales and planning can all be performed through Software as a Service. Businesses may wish to use one piece of software that performs all of these tasks or several that each perform different tasks. The required software can be subscribed to via the internet and then accessed online via any computer in the office using a username and password. If needs change they can easily switch to software that better meets their requirements. Everyone who needs access to a particular piece of software can be set up as a user, whether it is one or two people or every employee in a corporation that employs hundreds.