4.3 THE APPLICATIONS OF THE WEB 89 The name cloud derives from the cloud symbol that is usually used to represent the Internet in flowcharts and diagrams. Can you think of any examples of SaaS? In computing, runtime describes the period of time during which a program is running. Virtualisation is technology that allows users to use a machine s full capacity by distributing its capabilities among many users or environments. CLOUD COMPUTING Cloud computing is the delivery of services through the Internet including data storage, databases, networking and software. It works by enabling users to access data and applications over the Internet from remote physical servers, databases and computers. platform on which the application is running and without needing to install and run the application from their computer. Types of cloud computing Cloud computing can further be classified according to the way in which the services are offered. There are three types of cloud computing: Services A cloud may offer different types of services: Private cloud computing is a single-tenant environment where the hardware, storage and network are dedicated to a single client or company. Users usually pay a fixed amount for the service; Infrastructure as a Service (IaaS): it is the most basic model. Cloud providers offer essential storage and networking resources on demand; Platform as a Service (PaaS): providers offer computing platforms which include operating system, programming language, web server, databases and execution environment. Many providers even offer the possibility to increase or decrease CPU power depending on traffic loads; Public cloud computing is a multitenant environment in which a server shares the same hardware, storage and network devices as other users in the cloud. Users pay on a per-use basis; Hybrid cloud computing is a combination of at least two computing environments that share information and run the same applications. Those environments may include: one private cloud and one public cloud, two or more private clouds, two or more public clouds. Users pay for the portion of service (time/quantity) they use. Software as a Service (SaaS): providers deliver software applications over the Internet . Users get the access to application software without managing the infrastructure and User managed Service provider managed load: carico tenant: utente IaaS PaaS SaaS Application Application Application Data Data Data Runtime Runtime Runtime Operating System Operating System Operating System Virtualisation Virtualisation Virtualisation Servers Servers Servers Storage Storage Storage Networking Networking Networking 200 TelecoMMUNicaTioNs aND NeTWorKs Elettronica-Informatica.indb 200 25/01/24 16:09