Today the term cloud computing describes the abstraction of web-based computer, resources, and services that system developers can utilize to implement complex web-based system. In the simplest terms, cloud computing means storing and accessing data and programs over the Internet instead of your computer’s hard drive. The cloud is just a metaphor for the Internet. Cloud computing can be defined as a new style of computing in which dynamically scalable and often virtualized resources are provided as a service over the internet. With the cloud computing technology, users can use a variety of devices, including PCs, laptops, Smartphone to access programs, storage, and application-development platform over the internet, via services offered by cloud computing providers.
In phase 1, many users shared powerful mainframes using dummy terminals. In phase 2, stand-alone PCs became powerful enough to meet the majority of user’s needs. In phase 3, PCs, laptops, and servers were connected together through local networks to share resources and increase performance. In phase 4, local networks were connected to other local networks forming a global network such as the internet to utilize remote applications and resources. In phase 5, grid computing provided shared computing power and storage through a distributed computing system. In phase 6,cloud computing further provides shared resources on the internet in a scalable and simple way.
Comparing these sex computing paradigms, it looks like that cloud computing is a return to the original mainframe computing paradigm. However, these two paradigms have several important differences. Mainframe computing offers finite computing power, while cloud computing provides almost infinite power and capacity. In mainframe computing dummy terminals acted as user interface devices, while in cloud computing powerful PCs can provide local power and cashing support.
Cloud computing can be viewed as a collection of services, which can be presented as a layered cloud computing architecture. The services offered through cloud computing usually include IT services referred as:
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Saas (Software-as-a-Service), model provides a cloud-based foundation for software on demand. SaaS allows users to run applications remotely from the cloud. In general, a SaaS solution is web-delivered content that users’ access via a web browser. The advantages of SaaS solutions are simplicity of integration (users need only a browser), cost (the data center resides within the cloud), and scalability (customers can add user licenses or seats as needed). The Saas model presents a cloud-based application with a user interface to users running only a web browser. Well-known SaaS solution provides include Google Apps, Quick Books, etc.
IaaS (Infrastructure-as-a-Service) refers to computing resources as a service. This model provides a virtual data center within the cloud. This includes virtualized computers with guaranteed processing power and reserved bandwidth for storage and internet access. laaS provides servers, cloud-based data storage, and more.
Paas (Platform-as-a-Service) model provides the underlying hardware technology, such as one or more servers (or virtual servers), operating systems, database solutions, developer tools, and network support, for developers to deploy their own solutions. Developers need not worry about performing hardware or operating system upgrades. Instead, developers can focus on their own application. The hardware and software within a PaaS solution is managed by the platform provider. In other words, it is similar to laaS, but also includes operating systems and required services for a particular application.
Overall Figure of SaaS, IaaS and PaaS: