Course: Introduction to Computer Science Concepts and Programming (Texas A&M University)
Source: Cloud Computing overview document
Difficulty: Beginner Prerequisites: None. Basic familiarity with the internet and how applications work is helpful but not required.
Cloud computing is the delivery of computing resources (servers, storage, databases, networking, software) over the internet rather than from hardware you own and maintain locally. It is one of the foundational concepts in modern IT and comes up across nearly every area of computer science, from software engineering to cybersecurity. If you understand nothing else from this topic, understand that cloud computing replaces "buy and build your own infrastructure" with "rent what you need, when you need it." The three service models covered here (IaaS, PaaS, SaaS) describe how much of that stack the provider manages on your behalf.
Cloud computing delivers IT resources over the internet on a pay-per-use basis. The three main service models, IaaS, PaaS, and SaaS, differ in how much the cloud provider manages versus how much the customer controls. IaaS gives you raw infrastructure, PaaS gives you a ready-made development platform, and SaaS gives you a finished application.
Cloud computing
The on-demand delivery of computing services (servers, storage, networking, software) over the internet, typically on a pay-as-you-go pricing model.
Think of it as renting computing power instead of buying your own machines.
PaaS (Platform as a Service)
A cloud computing model that provides a complete development and deployment environment over the internet. A third-party host supplies the hardware and software tools, so developers can build applications without managing the underlying infrastructure.
In simple terms, PaaS is a ready-made workshop: the tools, the workbench, and the building are all provided. You just show up and build your app.
IaaS (Infrastructure as a Service)
A cloud computing model where a provider hosts fundamental computing resources (networking hardware, servers, storage) that would traditionally live in a physical data centre. The customer rents these resources and manages everything from the operating system upward.
Think of it as renting an empty server room: the provider keeps the lights on and the hardware running, but you install and manage everything else yourself.
SaaS (Software as a Service)
A software distribution model where applications are hosted by a provider (or by a third-party cloud provider on behalf of a software vendor) and made available to end users over the internet.
In simple terms, SaaS is any application you use through a browser or app without installing it locally. Google Docs, Slack, and Dropbox are everyday examples.
Load balancing
The process of distributing incoming network traffic across multiple servers so that no single server becomes overwhelmed. Commonly offered as part of IaaS.
Think of it as a queue manager directing customers to whichever checkout counter is least busy.
Data centre
A physical facility that houses networked computing equipment (servers, storage, networking hardware). Cloud providers operate large-scale data centres so their customers do not have to.
The models are best understood as layers of a stack. The further up the stack you go, the more the provider manages for you and the less control you have.
IaaS sits at the bottom. The provider manages the physical hardware, virtualisation, and networking. The customer manages the OS, middleware, runtime, data, and applications.
Resources include servers, storage, and networking hardware.
Additional services typically include log access, detailed billing, monitoring, security, and load balancing.
Use case: a company wants full control over its software environment but does not want to buy and maintain physical servers.
PaaS sits in the middle. The provider manages everything IaaS covers plus the operating system, middleware, and runtime.
Developers access the platform through a web browser.
Pricing is usage-based (pay for what you use).
Additional PaaS services include web service integration, information security tools, and development team collaboration features.
Use case: a development team wants to build and deploy a web application without worrying about server configuration or OS patches.
SaaS sits at the top. The provider manages the entire stack, including the application itself.
The end user simply accesses the finished application via a browser or app on any device.
The software vendor either hosts the application on its own cloud resources or uses a third-party cloud provider's data centre.
Use case: an office worker using a web-based email client or document editor.
There are two common arrangements:
The software provider hosts the application directly, using its own networking, computing, and database resources.
An independent software vendor partners with a third-party cloud provider, and the application runs in the cloud provider's data centre.
Either way, the result for the end user is the same: the application is accessible from any network or device.
IaaS: Amazon Web Services (AWS) EC2 lets companies rent virtual servers by the hour instead of buying and maintaining physical hardware.
PaaS: Heroku and Google App Engine let developers deploy web apps without configuring servers or installing operating systems.
SaaS: Gmail, Microsoft 365, and Salesforce are applications you use entirely through a browser, with nothing installed locally.
"IaaS and PaaS are the same thing." They are not. IaaS gives you raw infrastructure (virtual machines, storage). PaaS adds a managed development environment on top, so you skip OS and middleware configuration entirely. The dividing line is who manages the operating system.
"SaaS means the software is free." SaaS describes a delivery model, not a pricing model. Most SaaS products charge a subscription fee. The "service" refers to how it is delivered (over the internet, hosted by someone else), not to the cost.
"Cloud computing means your data is less secure." Cloud providers invest heavily in security infrastructure (encryption, monitoring, physical security) that most individual organisations could not replicate. Security risks in the cloud tend to come from misconfiguration on the customer's side, not from the model itself.
"You lose all control with cloud computing." The amount of control depends on the service model. IaaS gives you significant control over operating systems and applications. SaaS gives you the least. Choosing the right model is partly about choosing how much control you want to keep.
⚠️ Be able to distinguish IaaS, PaaS, and SaaS by what the provider manages versus what the customer manages. This is the most commonly examined point.
⚠️ Know which layer of the stack each model covers. A question that says "the customer manages the OS and applications, but not the hardware" is describing IaaS.
⚠️ Understand that SaaS can involve either the software vendor hosting directly or a third-party cloud provider hosting on the vendor's behalf.
⚠️ "Pay based on use" is a defining characteristic of cloud computing generally, but the source specifically associates it with PaaS.
True or false: PaaS requires the developer to install and configure their own operating system.
A: False. The PaaS provider manages the OS and runtime; the developer only manages the application and its data.
True or false: In SaaS, the end user must install the software on their own device.
A: False. SaaS applications are accessed via a browser or app over the internet.
Fill in the blank: IaaS provides virtualised versions of resources traditionally found in physical __________.
A: Data centres.
True or false: Load balancing is a service commonly associated with IaaS.
A: True.
Q: What are the three main cloud computing service models, and how do they differ?
A: IaaS (Infrastructure as a Service) provides raw computing resources such as servers and storage. PaaS (Platform as a Service) provides a development platform including the OS and middleware. SaaS (Software as a Service) provides finished applications to end users. They differ in how much of the computing stack the provider manages on the customer's behalf.
Q: A developer wants to build a web application without managing servers or operating systems. Which cloud service model is most appropriate?
A: PaaS, because it provides a managed development environment where the underlying infrastructure and OS are handled by the provider.
Q: Describe two ways a SaaS application can be hosted.
A: The software provider can host the application using its own networking, computing, and database resources. Alternatively, the software vendor can have its application hosted in a third-party cloud provider's data centre.
Q: Name three services typically offered by an IaaS provider beyond basic server hosting.
A: Log access, detailed billing, monitoring, security, and load balancing (any three).
Q: Why is cloud computing described as "pay based on use"?
A: Users pay only for the resources they consume rather than purchasing and maintaining their own physical infrastructure. This usage-based pricing means costs scale with demand.
This material connects directly to computer networking, since cloud services depend entirely on internet connectivity and protocols such as HTTP/HTTPS. It also relates to software engineering and DevOps, where PaaS platforms are a standard part of modern deployment pipelines. If your course covers virtualisation later, that topic underpins how IaaS providers offer isolated virtual machines on shared physical hardware.
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