What is cloud computing?

Cloud computing provides resources such as servers, storage, networking and software over a network on demand. Physical hardware has not disappeared: resources run in data centres. Users can access them without purchasing every component themselves.

How do IaaS, PaaS and SaaS differ?

IaaS supplies infrastructure such as virtual machines and networks, leaving substantial operating-system and application management with the customer. PaaS provides a more prepared application development and execution environment. SaaS offers ready-to-use software. Elasticity can make capacity easier to increase or reduce with demand, but scaling is neither unlimited nor always instantaneous: quotas and technical limits remain. Public, private and hybrid arrangements meet different ownership and deployment needs. Not every remotely hosted server necessarily exhibits all cloud characteristics.

How are costs and security responsibilities shared?

Usage-based charging may reduce initial investment without automatically reducing total cost. Data transfer, storage, backups and idle resources can all generate charges. Provider security does not remove customer responsibility for access rights and data configuration. Outages, connectivity loss and migration to another provider require planning. Data location and the ability to retrieve information also matter. A file in the cloud is not by itself a reliable backup without version retention and an independent recovery plan.