Evolution of Cloud Computing
The trend toward cloud computing started in the late 1980s with the concept of grid computing when, for the first time, a large number of systems were applied to a single problem, usually scientific in nature and requiring exceptionally high levels of parallel computation. In Europe , long distance optical networks are used to tie multiple universities into a massive computing grid in order that resources could be shared and scaled for large scientific calculations.
Grid computing provided a virtual pool of computation resources but it's different than cloud computing. Grid computing specifically refers to leveraging several computers in parallel to solve a particular, individual problem, or to run a specific application. Cloud computing, on the other hand, refers to leveraging multiple resources, including computing resources, to deliver a unified “service” to the end user.
In grid computing, the focus is on moving a workload to the location of the needed computing resources, which are mostly remote and are readily available for use. Usually a grid is a cluster of servers on which a large task could be divided into smaller tasks to run in parallel. From this point of view, a grid could actually be viewed as just one virtual server. Grids also require applications to conform to the grid software interfaces.
In a cloud environment, computing and extended IT and business resources, such as servers, storage, network, applications and processes, can be dynamically shaped or carved out from the underlying hardware infrastructure and made available to a workload. In addition, while a cloud can provision and support a grid, a cloud can also support non-grid environments, such as a three-tier Web architecture running traditional or Web 2.0 applications
In the 1990s, the concept of virtualization was expanded beyond virtual servers to higher levels of abstraction—first the virtual platform, including storage and network resources, and subsequently the virtual application, which has no specific underlying infrastructure. Utility computing offered clusters as virtual platforms for computing with a metered business model.
More recently software as a service (SaaS) has raised the level of virtualization to the application, with a business model of charging not by the resources consumed but by the value of the application to subscribers. The concept of cloud computing has evolved from the concepts of grid, utility and SaaS. It is an emerging model through which users can gain access to their applications from anywhere, at any time, through their connected devices. These applications reside in massively scalable data centers where compute resources can be dynamically provisioned and shared to achieve significant economies of scale.
Companies can choose to share these resources using public or private clouds, depending on their specific needs. Public clouds expose services to customers, businesses and consumers on the Internet. Private clouds are generally restricted to use within a company behind a firewall and have fewer security exposures as a result. The strength of a cloud is its infrastructure management, enabled by the maturity and progress of virtualization technology to manage and better utilize the underlying resources through automatic provisioning, re-imaging, workload rebalancing, monitoring, systematic change request handling and a dynamic and automated security and resiliency platform.
As more enterprises add cloud computing the level of applications is migrating toward more mission critical and SaaS will become a mainstay of IT strategies.
A number of companies, including Google, Microsoft, Amazon, and IBM, have built enormous datacenter-based computing capacity all over the world to support their Web service offerings (search, instant messaging, web-based retail). With this computing infrastructure in place these companies are already poised to offer new cloud-based software applications.
Large enterprise software solutions, such as ERP (Enterprise Resource Planning) applications, have traditionally only been affordable to very big enterprises with big IT budgets. However, companies that sell these solutions are finding they can reach small to medium businesses by making their very expensive, very complex applications available as Internet-based software services. This ability of SaaS to deliver expensive applications at affordable will continue to accelerate.