MS-900 Describe cloud concepts Practice Question
A company uses a cloud service where they can provision virtual machines, install any operating system, and manage all software on those machines. The cloud provider is responsible for the physical hardware, data center security, and network infrastructure. Which cloud service model does this represent?
⚠ Common exam trap
Candidates often confuse IaaS with PaaS because both involve virtual machines, but the key differentiator is whether the customer manages the operating system and software stack (IaaS) or the provider manages them (PaaS).
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IaaS (Infrastructure as a Service)
This scenario describes Infrastructure as a Service (IaaS) because the customer has full control over virtual machines, including the operating system and all installed software, while the cloud provider manages the underlying physical hardware, data center security, and network infrastructure. In IaaS, the provider offers virtualized computing resources over the internet, and the customer is responsible for everything above the hypervisor layer, such as OS patches, application configuration, and middleware.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
IaaS (Infrastructure as a Service)
Why this is correct
In the Infrastructure-as-a-Service model, the cloud provider supplies fundamental computing resources such as virtual machines, storage, and virtual networks on demand. Subscribers can provision these VMs with their own operating system, middleware, and applications, retaining administrative control over the OS, security patching, and software configuration while the provider maintains the physical host hardware and datacenter infrastructure. This directly matches the scenario of provisioning a virtual machine.
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PaaS (Platform as a Service)
Why it's wrong here
Platform as a Service abstracts away the underlying OS and runtime environment, offering a fully managed hosting platform that includes compute scaling, databases, development tools, and middleware. The customer only writes and deploys applications and manages data, whereas the provider handles OS updates, patching, and infrastructure capacity. Because the scenario involves provisioning virtual machines and thus controlling the OS, PaaS is not the correct model.
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SaaS (Software as a Service)
Why it's wrong here
Software as a Service delivers a complete, production-ready application over the internet, with the provider operating the entire stack - infrastructure, OS, middleware, app code, and data storage - behind the scenes. Subscribers simply sign in and use the software without provisioning any virtual machines or making infrastructure decisions. The absence of any VM provisioning separates this scenario from Microsoft 365-style SaaS delivery.
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FaaS (Function as a Service)
Why it's wrong here
Function as a Service is an event-driven, serverless compute model in which a provider executes individual code functions in response to triggers (such as HTTP requests or queue messages), automatically scaling them to zero when idle. The customer never provisions or manages servers, and there is no persistent OS to control or patch. Since the question describes provisioning a virtual machine and retaining OS control, FaaS is an incorrect match.
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