A1.1.9 · Computer hardware and operation
Cloud services
By the end you can
Describe SaaS, PaaS and IaaS: what each provides, who manages what, and the trade-offs of each.
means using computing resources (software, development platforms, servers, storage) that belong to someone else and are reached over the internet. Instead of buying hardware up front, an organisation rents what it needs and pays for what it uses. Behind the scenes, providers run huge data centres and use to share each physical machine between many customers.
Cloud services come in three main models. They differ in how much the provider manages for you, and so how much control you keep.
- Applicationyou
- Datayou
- Runtimeyou
- Middlewareyou
- Operating systemyou
- Virtualisationprovider
- Serversprovider
- Storageprovider
- Networkingprovider
IaaS
You rent virtual machines, storage and networks. You install and look after the operating system and everything above it.
You manage 5 of 9 layers. Further right means less work and less control: the provider handles more, and you can change less.
The three models#
SaaS
Software as a Service
Ready-to-use applications over the internet, usually in a browser, often on a subscription.
Examples: Online office suites and email (such as Google Workspace or Microsoft 365), online accounting, video calling.
+ Nothing to install or maintain; updates arrive automatically; use it from any device.
− Unusable without internet; your data sits with the provider; little control over features.
PaaS
Platform as a Service
A platform for developers to build, test, deploy and scale their own applications, with the operating system, runtime, databases and tools provided.
Examples: App hosting platforms such as Microsoft Azure App Service, Google App Engine or Heroku.
+ Developers focus on code, not servers; easy to scale as users grow.
− Less control of the environment; vendor lock-in can make moving to another provider hard.
IaaS
Infrastructure as a Service
Virtualised computing resources: virtual machines, storage and networks, rented instead of bought.
Examples: Virtual servers such as Amazon EC2, Microsoft Azure Virtual Machines or Google Compute Engine.
+ Full control of the machines; no hardware to buy; scale up or down in minutes.
− You manage and secure the OS and software yourself, which needs expertise; costs can creep up.
In short: with you use software, with you build software on someone else's platform, and with you rent the machines and build everything on them yourself.
A school uses an online office suite for email, documents and shared folders.
A start-up uploads its web app’s code and lets the platform handle servers and scaling.
A company rents virtual servers and installs its own operating system and database software.
A researcher rents 50 powerful virtual machines for a week to run a big simulation, configured exactly as she needs.
A shop pays monthly for an online accounting package.
A developer builds an app on a platform that provides the database, runtime and deployment tools.
0 / 6 right
Why use the cloud at all?#
- Low up-front cost: no servers to buy; pay monthly or by usage.
- : add capacity in minutes for a busy period, and drop it afterwards.
- Less maintenance: the provider handles hardware failures, power, cooling and (depending on the model) updates.
- Access anywhere, from any device with an internet connection.
And the costs:
- It depends on a reliable internet connection and on the provider staying up.
- Data is held by a third party, which raises security, privacy and legal questions (where in the world is it stored?).
- Ongoing fees can exceed the cost of owning hardware over time, and can make switching providers expensive.
Check yourself
Cloud service models
Quick questions, made fresh every time and marked here. Do a few until they feel easy.
Exam practice
Paper 1-style questions
4 questions · 14 marks
Write your answer as you would in the exam, then show the mark points and tick each one your answer made. These are our own questions in the style of the exam, not past-paper questions.
1.Describe Software as a Service (SaaS), giving an example.
[2]Describe: A detailed account: say what happens, step by step if it is a process.
2.Explain one advantage and one disadvantage of Infrastructure as a Service (IaaS) for a growing company.
[4]Explain: Give reasons: say what happens AND why, or how one thing causes another.
3.Distinguish between Platform as a Service (PaaS) and Infrastructure as a Service (IaaS).
[2]Distinguish: Make the differences between two things clear.
4.A small school runs its own email and file servers, looked after by one part-time technician. Evaluate moving to a SaaS office suite with cloud email and file storage.
[6]Evaluate: Weigh the strengths against the weaknesses (or the benefits against the costs) and reach a judgement that you back up.
Past papers
Old exam questions on this topic
From HL Paper 1, May 2014 to November 2025. These papers were set on the previous syllabus, so the wording may differ from today's exam, but the topic is the same. Find the questions and markschemes in your school's past-paper pack.
| Paper | Question | Marks | About |
|---|---|---|---|
| November 2025 | 12(c) | 6 | Local versus cloud storage |
| May 2024 TZ1 | 1 | 2 | One benefit and one drawback of SaaS |
| May 2014 | 12(a) | 3 | Features of SaaS |
| May 2014 | 12(b) | 6 | SaaS and security |
In a nutshell
- Cloud computing: using computing resources over the internet from a provider, paying as you go, instead of owning them.
- SaaS: finished software used in a browser (online office suites, web email). Easiest to use, least control; needs internet, data held by the provider.
- PaaS: a platform to build and run your own apps without managing servers or the OS. Faster development; risk of vendor lock-in.
- IaaS: rented virtual machines, storage and networks; you manage the OS and above. Most control and flexibility; needs the most expertise.
- All three: little up-front cost and easy scaling, but dependence on the internet and on the provider’s security and reliability.