Understanding cloud: IaaS, PaaS, SaaS
This page presents the main cloud service models, their differences and how responsibilities shift between the organisation and the provider.
What is cloud?
Cloud means using computing resources as services: compute, storage, networking, databases, technical platforms or software.
Instead of running the whole infrastructure in-house, part of the chain is handled by a provider. The exact scope depends on the model chosen.
The three most common terms are IaaS, PaaS and SaaS. They represent three different service levels and therefore three different ways of sharing responsibilities.
Key points
- The higher the service level, the less infrastructure is operated directly.
- Data, access management and integrations remain important topics.
- Cloud does not remove operational needs, it shifts part of them elsewhere.
Cloud service models
Three common ways to understand what remains under the organisation’s responsibility and what is handled by the provider.
On-premises
The organisation operates the entire stack: infrastructure, systems, middleware, data and applications.
IaaS
The provider delivers the infrastructure. The organisation keeps control of systems, services and applications.
PaaS
The provider also handles part of the platform. The organisation focuses more on applications and data.
SaaS
The application is delivered as a service. The organisation mainly focuses on usage, access, data and integration.
Shared responsibilities
A concise view of technical layers depending on the model selected.
| Technical layers | On-premises | IaaS | PaaS | SaaS |
|---|---|---|---|---|
| Business applications Functional scope, configuration, usage | ||||
| Data Content, quality, lifecycle | ||||
| Integration APIs, flows, synchronisation | ||||
| Databases Engines, operations, logical backups | ||||
| System and middleware Linux, runtimes, technical services | ||||
| Infrastructure Servers, storage, network, virtualisation |
The exact split varies depending on the services selected, but this table provides a useful reading guide.
What the chosen model changes
The more technical layers are handled by the provider, the more the organisation focuses on applications, data and usage.
In return, the room for action on some technical components may become more limited.
Why this distinction matters
IaaS, PaaS and SaaS are not just commercial labels. They help clarify who operates what, and which technical layers are affected by architectural choices.
This way of reading things makes it easier to compare cloud services that may look similar at first glance.