Date Posted : 2 years ago

The concept of cloud computing is to offer the entire range of services as individual services ("as a service"). Based on the five technology features listed above (cf. Section 3), the user is thus given the most excellent possible flexibility in using individual or multiple IT services. There are three levels of IT services provided as cloud services (Mell & Grance, 2011) (BITKOM, 2009).

  • "Infrastructure as a Service" (IaaS): This primarily involves the provision of computing and storage power on virtualized servers and the necessary network infrastructure, which companies offer on a usage-dependent basis (example: Amazon Web Services).
  • "Platform as a Service" (PaaS): A layer above the infrastructure components, services describe the provision of development services, e.g., operating systems, language interpreters, or Web servers on which developers can create their applications and execute code (example: Windows Azure).
  • "Software as a Service" (SaaS): The actual applications are located on the top level. They address themselves directly to the user as ready-made software solutions and can be accessed by navigating in a web browser (example: Google Apps).
The three levels are arranged hierarchically, but their boundaries are often not clearly defined. Infrastructure services form the basis for platform services, which in turn form the basis for software applications.

Infrastructure services contain the virtual infrastructure resources with a pre-installed operating system, which are based on the provider's networked hardware resource pool. Platform services also provide a database and a service layer (middleware) for switching to the applications installed. Such requests are only part of the service provided in the case of software services. Depending on the field of application, an agreed level of resources is made available by the provider and the levels arranged above it are given to the user's area of responsibility