The answer is Infrastructure as a Service (IaaS). IaaS delivers virtualized computing resources over the internet, giving you full control over the guest operating system and the ability to install custom software, while the cloud provider manages the underlying physical hardware like servers, storage, and networking. This distinction is critical for the Microsoft Azure Fundamentals AZ-900 exam, which tests your ability to match business requirements to the correct cloud service model. A common trap is confusing IaaS with PaaS, but remember that PaaS abstracts away the OS layer to focus on application deployment, and SaaS delivers fully managed software. If you need OS control without hardware management, IaaS is the only fit. Memory tip: think “I” in IaaS stands for “I control the OS,” while “P” in PaaS stands for “Platform only,” and “S” in SaaS stands for “Software, no control.”
AZ-900 Describe cloud concepts Practice Question
This AZ-900 practice question tests your understanding of describe cloud concepts. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is evaluating cloud service models. They need to migrate an existing application that requires full control over the operating system and custom software installations. They do not want to manage the underlying physical hardware. Which cloud service model best fits this requirement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Correct. IaaS provides virtualized compute resources. The customer is responsible for the OS, applications, and middleware, while the provider manages the physical infrastructure.
B
Platform as a Service (PaaS)
Why wrong: Incorrect. PaaS manages the OS and runtime, so the customer does not have full control over the operating system.
C
Software as a Service (SaaS)
Why wrong: Incorrect. SaaS provides a fully managed application. The customer only uses the software and has no control over the underlying OS or infrastructure.
D
On-premises deployment
Why wrong: Incorrect. On-premises requires managing physical hardware, which the company explicitly wants to avoid.
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)
Infrastructure as a Service (IaaS) provides virtualized computing resources over the internet, including virtual machines with full control over the guest operating system. This allows the company to install custom software and manage the OS while the cloud provider handles the underlying physical hardware, such as servers, storage, and networking. The requirement for full OS control and custom software installations excludes PaaS and SaaS, which abstract away the OS layer.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Correct. IaaS provides virtualized compute resources. The customer is responsible for the OS, applications, and middleware, while the provider manages the physical infrastructure.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Platform as a Service (PaaS)
Why it's wrong here
Incorrect. PaaS manages the OS and runtime, so the customer does not have full control over the operating system.
✗
Software as a Service (SaaS)
Why it's wrong here
Incorrect. SaaS provides a fully managed application. The customer only uses the software and has no control over the underlying OS or infrastructure.
✗
On-premises deployment
Why it's wrong here
Incorrect. On-premises requires managing physical hardware, which the company explicitly wants to avoid.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse PaaS with IaaS because both involve cloud hosting, but PaaS removes OS-level access, making it unsuitable for scenarios requiring custom software installations or full OS control.
Detailed technical explanation
How to think about this question
Under the hood, IaaS delivers virtual machines (VMs) via hypervisors such as Hyper-V or KVM, with the provider managing the physical host and storage area networks (SANs). The customer retains full administrative access to the VM via Remote Desktop Protocol (RDP) or SSH, enabling OS-level configuration, patching, and installation of any software stack (e.g., custom databases or legacy applications). In a real-world scenario, migrating an on-premises ERP system with specific OS dependencies would require IaaS to preserve control while offloading hardware maintenance.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-900 question in full detail.
Describe cloud concepts — This question tests Describe cloud concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Infrastructure as a Service (IaaS) — Infrastructure as a Service (IaaS) provides virtualized computing resources over the internet, including virtual machines with full control over the guest operating system. This allows the company to install custom software and manage the OS while the cloud provider handles the underlying physical hardware, such as servers, storage, and networking. The requirement for full OS control and custom software installations excludes PaaS and SaaS, which abstract away the OS layer.
What should I do if I get this AZ-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company wants to use a cloud service that provides a fully managed database, including automated backups, patching, and high availability, without managing any underlying servers. Which cloud service model is this?
easy
A.Infrastructure as a Service (IaaS)
✓ B.Platform as a Service (PaaS)
C.Software as a Service (SaaS)
D.Container as a Service (CaaS)
Why B: This scenario describes a fully managed database service where the provider handles backups, patching, and high availability, and the customer does not manage any underlying servers. This is the definition of Platform as a Service (PaaS), which provides a managed platform (including database engines like Azure SQL Database) where the customer only manages data and schema, while the provider handles the OS, runtime, and infrastructure.
Variation 2. Which type of cloud service model would a company typically use for hosting their own custom web application where they manage the code but not the server operating system?
medium
A.IaaS (Infrastructure as a Service)
✓ B.PaaS (Platform as a Service)
C.SaaS (Software as a Service)
D.FaaS (Function as a Service)
Why B: PaaS (Platform as a Service) is correct because the company manages only the application code and data, while the cloud provider handles the underlying server operating system, runtime, middleware, and infrastructure. This aligns with the scenario where the customer controls the custom web application but not the OS.
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Question Discussion
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