In cloud computing architecture, which different layers are commonly used to describe the overall cloud architecture stack, from underlying hardware up to the application that the end user interacts with?

Introduction / Context:
Cloud computing architecture is often explained in terms of layers. These layers help learners understand how responsibilities are separated between physical resources, virtualised infrastructure, developer platforms, and the final application that the user sees. This question checks whether you know the standard layered view of cloud architecture, which is very important for interviews and certification exams related to cloud computing and system design.

Given Data / Assumptions:

• We are talking about general cloud computing architecture, not a specific vendor implementation.
• The focus is on conceptual layers, not on individual services or products.
• The typical reference model has a bottom to top view starting from hardware and going up to the application.

Concept / Approach:
In many textbooks and training materials, cloud architecture is described as a stack of layers. At the bottom there is physical hardware such as servers and network devices. Above that sits infrastructure, which provides virtual machines, storage, and networking as Infrastructure as a Service. On top of that, the platform layer offers runtime environments, databases, and development frameworks as Platform as a Service. Finally, the application layer provides finished applications to end users as Software as a Service. Understanding this layered view helps you reason about who manages which part, and how responsibilities are divided between cloud provider and consumer.

Step-by-Step Solution:
Step 1: Identify the typical bottom layer in cloud computing, which is the physical hardware in the data centre such as servers, storage devices, and networking equipment. Step 2: Recognise that above the hardware, cloud providers offer infrastructure capabilities like virtual machines, virtual networks, and block storage, often referred to as the infrastructure layer. Step 3: Understand that the next layer is the platform layer, which provides application runtimes, managed databases, message queues, and developer tools. Step 4: At the top, the application layer delivers complete applications such as webmail, CRM systems, or collaboration tools directly to end users. Step 5: Compare the options and select the one that clearly lists hardware, infrastructure, platform, and application as the four main layers of cloud architecture.

Verification / Alternative check:
A quick way to verify the answer is to map these layers to the familiar service models: hardware plus infrastructure roughly align with Infrastructure as a Service, the platform layer aligns with Platform as a Service, and the application layer aligns with Software as a Service. If a description can be grouped this way, it is very likely referring to the standard layered cloud stack and is therefore correct in this context.

Why Other Options Are Wrong:
Option B: Describes only a single virtualisation layer and ignores platform and application layers, so it is incomplete and does not match standard cloud architecture. Option C: Talks about database, spreadsheet, and presentation layers, which relate to office productivity software, not cloud architecture. Option D: Mentions router, switch, and firewall layers, which are networking components but not the conceptual layers of cloud computing architecture.

Common Pitfalls:
Learners sometimes confuse networking components or software layers in an application with cloud architecture layers. Another common mistake is to think only in terms of service models like Software as a Service and Infrastructure as a Service without connecting them to the underlying architectural layers. Keeping a clear mental picture of hardware, infrastructure, platform, and application as separate but related layers helps avoid such confusion.

Final Answer:
The correct description of the layers that define cloud computing architecture is Hardware, infrastructure, platform, and application layers working together in a stack.