Cloud computing & service models (IaaS / PaaS / SaaS)
What it is
Cloud computing is delivering computing services — servers, storage, databases, networking, software, analytics — over the internet by the second, from someone else’s data centers. The three primary service models describe how much you manage vs. the provider:
| You manage | Provider manages | Example | |
|---|---|---|---|
| IaaS (Infrastructure) | OS, apps, data | VMs, storage, network, hypervisor | VMs |
| PaaS (Platform) | your app & data | the platform, runtime, scaling | App Service, Functions |
| SaaS (Software) | just usage | everything | Microsoft 365, Azure DevOps |
Why it exists
You stop buying/operating physical hardware and instead rent exactly what you need, scale it on demand, and pay only for what you use. That changes the economics and ops of running software.
Key ideas
- IaaS — most control, most operational work (you patch the OS).
- PaaS — you focus on code; the platform handles scale/infra.
- SaaS — fully managed; you just sign in and use it.
- This distinction is fundamental for the whole exam — every service you meet (
[[azure-vm|VM]]=IaaS,[[app-service|App Service]]=PaaS,[[azure-functions|Functions]]=serverless/PaaS) slots into it.
Exam notes
- Know which model each service is: VMs = IaaS, App Service/Functions/CI = PaaS/serverless, Microsoft 365/Azure Boards = SaaS.
- The “managed services vs managed-by-you” boundary is a frequent exam discriminator.
Related
azure-vm · app-service · azure-functions · resource-group · arm
📘 Source: Microsoft — Types of cloud computing (IaaS/PaaS/SaaS)