Answer: “Cloud Computing” is a somewhat nebulous word to describe users “renting” or borrowing online software instead of actually purchasing and installing it on their own computers. It is the same business model as people using Gmail or Yahoo mail services, except that cloud computing goes much further. Cloud computing is where entire businesses and thousands of employees will run their computer tools as online rented products. All of the processing work and file saving will be done “in the cloud” of the Internet, and the users will plug into that cloud every day to do their computer work.
Cloud computing has two major premises:
- Software as a Service (aka “Saas” or “SaS”)
- Platform as a Service (aka “PaaS” or “PaS”)
Software and Platform as a Service describe the business model of users logging into a centralized hub to access their software products. Users open their files and software only while online, using only their web browser and passwords. It is similar to the idea of mainframe terminals, but cloud computing involves a much larger “cloud” (network) of processing computers at the center.
Software as a service (SaaS) instead of selling you a copy of Microsoft Word for $300, a cloud computing model would “rent” word processing software to you through the Internet for perhaps 5 dollars a month. You would not install any special software, nor would you be confined to your home machine to use this rented online product. You simply use your modern web browser to login from any web-enabled computer, and you can access your word processing documents in the same way that you would access your Gmail.
Platform as a service (PaaS) is a category of cloud computing services that provide a computing platform and a solution stack as a service. Along with SaaS and IaaS, it is a service model of cloud computing. In this model, the consumer creates the software using tools and libraries from the provider. The consumer also controls software deployment and configuration settings. The provider provides the networks, servers and storage.
There is a third premise however – Infrastructure as a Service (IaaS) Infrastructure as a Service refers to a combination of hosting, hardware, provisioning and basic services needed to run a cloud. The IaaS is the part of the cloud computing architecture that provides access over the Internet. Bandwidth allocation and server resources are essential elements of IaaS. The IaaS architecture specifies dynamic scaling of bandwidth. A cloud computing installation should never be overwhelmed by peak demand, because the infrastructure service should be able to quickly add the resources needed to accommodate peak demand.
- IaaS - the unit you are gaining is a computer/server. Therefore IaaS is essentially a “physical server box”. An example of this would be going to RackSpace or SoftLayer and leasing a physical box from them. The vendor manages the networking, hard drives (if they fail), hardware of the box, virtualization O/S (if the box is virtualized). You can remote desktop to the box and you manage everything else (shown in the screenshot above). Windows Azure provides IaaS in the form the VM Role (you upload a Windows Server 2008 R2 image and manage the server yourself).
- PaaS - the unit you are gaining is an application/framework. Therefore PaaS is a “hosted application/framework/tools that you can leverage to build something on. That application is configured on IIS/SQL Server etc and runs on a hardware/virtual system that the vendor manages. An example of PaaS would be Windows Azure (excluding the VM Role) services like web role, worker role, Reporting Services etc.
- SaaS - the unit you are gaining is business functionality. For example, Gmail is a type of a SaaS mail provider because you don’t have to manage any service yourself and its all done by the vendor (Google in this example).