The Infrastructure Layer

Cloud: Cloud computing is a kind of Internet-based computing that provides shared processing resources and data to computers and other devices on demand. It is a model for enabling ubiquitous, on-demand access to a shared pool of configurable computing resources. This shared pool of configurable computing resources could include networks, servers, storage, applications and services, and it can be rapidly provisioned and released with minimal management effort. (Wikipedia, edited by SH)

Software Defined: Software defined is, effectively, another term for virtualisation. It is often applied to a specific area of technology; thus “software-defined networking” or “software-defined datacentre”. With a software-defined technology, all infrastructure is virtualised and delivered as a service. The control of the hardware is fully automated in software, so hardware configuration is maintained through the programming of intelligent software systems, instead of being defined by physical hardware and devices. Programmed or software-defined technology is particularly appropriate to the integration or orchestration of legacy enterprise applications and new cloud computing services. (DN)

Virtualisation: The main enabling technology for cloud computing is virtualisation. Virtualisation software separates a physical computing device into one or more “virtual” devices, each of which can be easily used and managed to perform computing tasks. With operating system-level virtualisation essentially creating a scalable system of multiple independent computing devices, idle computing resources can be allocated and used more efficiently. Virtualisation provides the agility required to speed up IT operations, and reduces cost by increasing infrastructure utilisation. (Wikipedia)