MS-900 Describe cloud concepts Practice Question
A company subscribes to a cloud service where they can provision virtual machines, choose the operating system, install any software, and manage all applications. The cloud provider is responsible for the underlying physical hardware and network infrastructure. Which cloud service model is being used?
⚠ Common exam trap
Candidates often confuse IaaS with PaaS because both involve virtual machines, but PaaS abstracts the OS and runtime, whereas IaaS gives the customer full control over the OS and software installation, as explicitly stated in the question.
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
✓
Infrastructure as a Service (IaaS)
This scenario describes Infrastructure as a Service (IaaS) because the customer provisions virtual machines, chooses the operating system, installs software, and manages applications, while the cloud provider is responsible for the underlying physical hardware and network infrastructure. In IaaS, the provider delivers virtualized computing resources over the internet, and the customer retains control over the OS, storage, and deployed applications, which matches the description exactly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Infrastructure as a Service (IaaS)
Why this is correct
IaaS is correct because the provider supplies virtualized compute, storage, and networking on physical servers it owns and operates, while customers provision these resources as virtual machines and install their own operating systems, runtime environments, and applications. This gives customers the same administrative control over the OS and application stack as they would have on physical servers, without needing to manage datacenter hardware, cooling, or power. The ability to define the OS version, configure its settings, and deploy arbitrary software exactly matches the scenario's description of controlling both OS and applications.
- ✗
Platform as a Service (PaaS)
Why it's wrong here
PaaS is wrong for this scenario because it strips away OS-level control: the provider fully manages the operating system, runtime, and middleware, and the customer merely deploys application code into a managed hosting environment. Customers do not provision virtual machines, choose a specific OS image, patch the OS, or configure its internal settings, which contradicts the requirement that the customer controls the OS and applications. Even though PaaS is a cloud service, its fundamental abstraction of the platform makes it an incorrect fit.
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Software as a Service (SaaS)
Why it's wrong here
SaaS is wrong because it delivers a completely finished application (such as email or CRM) over the internet, with the provider managing the entire stack—servers, OS, storage, and app updates. The customer only configures business settings and manages data, without ever provisioning infrastructure or controlling the OS itself. This directly contradicts the described scenario where the customer retains control of the OS and applications, so SaaS cannot be the answer.
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On-premises
Why it's wrong here
On-premises is wrong because it is not a cloud service at all: the customer owns, installs, and maintains all physical hardware, virtualization layer, operating systems, and applications entirely within their own facilities. The scenario explicitly states a subscription to a cloud service, which implies that a third-party provider hosts and delivers resources over the internet, eliminating the need for the customer to manage physical infrastructure. Thus, on-premises in no way matches the provisional, provider-managed nature of the described environment.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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