SaaS vs on-premise vs PaaS vs IaaS — what is the difference?
These terms describe how much of the technology stack a provider operates for you. On-premise means you own and run everything: hardware, operating system, runtime and application. Infrastructure as a Service (IaaS) provides virtual machines, storage and networking. Platform as a Service (PaaS) adds the operating system and runtime, so you deploy code while the provider manages the servers. Software as a Service (SaaS) is a complete product that you sign in to and use, with the provider operating every layer.
Each step up reduces operational work, such as patching, scaling, backups and failover, in exchange for less control over how it is done. The right choice often differs between systems within the same organisation.
For example, a business might use SaaS for email, deploy its customer-facing application on PaaS and run a specialised data-processing workload on IaaS. Combining models in this way is common.
A useful test is to ask who responds when the system fails. If it is the vendor, it is SaaS. If it is your team on infrastructure you do not own, it is IaaS or PaaS. If your team also owns the hardware, it is on-premise.
For businesses commissioning custom software, the key decision is usually between PaaS and IaaS for the application being built.
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Custom SaaS DevelopmentMulti-tenant platforms with billing, administration and access control built in.
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