Cloud computing is the delivery of computing services such as servers, storage, databases, networking, software, and analytics over the Internet, commonly referred to as "the cloud". Instead of owning and maintaining physical computers and servers, individuals and organisations rent computing power and storage from cloud providers and pay only for what they use. This model has completely transformed the way businesses operate, making powerful computing available to everyone, from a small startup to a multinational corporation.
The National Institute of Standards and Technology (NIST) defines cloud computing as a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort. The cloud is built on the concept of virtualisation, where physical servers are divided into multiple virtual machines that can run independently. Users access these resources through a browser or an application, without worrying about the underlying hardware.
In this chapter we will study the characteristics and benefits of cloud computing, its service models such as IaaS, PaaS, and SaaS, its deployment models such as public, private, hybrid, and community clouds, and its advantages and disadvantages. We will also look at real-world examples of cloud services like Google Drive, Microsoft Azure, and Amazon Web Services. This chapter connects networking, web services, and databases into a complete picture of modern IT infrastructure.
2. Characteristics of Cloud Computing
Cloud computing has several essential characteristics that distinguish it from traditional computing.
On-demand self-service: Users can provision computing resources such as servers and storage automatically without requiring human interaction with the service provider.
Broad network access: Resources are available over the network and can be accessed from laptops, mobiles, and tablets using standard protocols.
Resource pooling: The provider's resources are pooled to serve multiple users, with virtual and physical resources assigned dynamically according to demand.
Rapid elasticity: Resources can be scaled up or down quickly and elastically to meet changes in demand.
Measured service: Cloud systems automatically monitor and control resource usage, and users are billed only for what they actually use.
These five characteristics, defined by NIST, are the essence of the cloud model and are frequently tested in examinations.
3. Service Models of Cloud Computing
Cloud services are offered in three main service models, depending on the level of control the user needs.
IaaS (Infrastructure as a Service)
IaaS provides the fundamental computing resources such as virtual machines, storage, and networking over the Internet. The user has control over the operating system, storage, and deployed applications, but not over the underlying physical infrastructure. Examples include Amazon EC2, Microsoft Azure Virtual Machines, and Google Compute Engine. IaaS gives the maximum control to the user.
PaaS (Platform as a Service)
PaaS provides a platform where developers can build, test, and deploy applications without worrying about the underlying infrastructure. It includes the operating system, programming language execution environment, database, and web server, all managed by the provider. Examples include Google App Engine, Microsoft Azure App Services, and Heroku. PaaS is ideal for developers who want to focus only on writing code.
SaaS (Software as a Service)
SaaS delivers complete software applications over the Internet on a subscription basis. The user does not manage the application, operating system, or hardware; they simply use the software through a browser. Examples include Google Drive, Google Docs, Microsoft Office 365, and Gmail. SaaS is the most common cloud model used by everyday users.
4. Deployment Models of Cloud Computing
Based on who owns and controls the cloud, deployment models are classified as follows.
Public cloud: The cloud infrastructure is owned by a third-party provider and is available to the general public over the Internet. It is the most cost-effective model. Examples include AWS and Google Cloud.
Private cloud: The cloud infrastructure is used exclusively by a single organisation. It can be managed by the organisation itself or by a third party, and offers the highest security and control.
Hybrid cloud: A combination of public and private clouds that allows data and applications to be shared between them. Organisations keep sensitive data in the private cloud and use the public cloud for other workloads.
Community cloud: The infrastructure is shared by several organisations with common concerns, such as security or compliance, for example the banks of a country.
The choice of deployment model depends on cost, security, and regulatory requirements.
5. Virtualisation
Virtualisation is the technology that makes cloud computing possible. It is the process of creating a virtual version of physical resources such as servers, storage, or networks. A physical server can be divided into several virtual machines (VMs), each with its own operating system, running independently on the same hardware. The software that manages this division is called a hypervisor.
Virtualisation offers many benefits: better utilisation of hardware, lower costs, easier management, faster provisioning, and isolation between tenants. Because of virtualisation, cloud providers can pool their physical resources and serve thousands of customers from a single data centre. Virtualisation and cloud computing together form the backbone of modern data centres.
6. Advantages of Cloud Computing
Cost savings: No need to buy expensive hardware; pay only for resources used.
Scalability: Resources can be increased or decreased instantly according to demand.
Accessibility: Data and applications can be accessed from anywhere in the world using any device with an Internet connection.
Automatic updates: The provider manages software updates and security patches.
Reliability and backup: Data is stored redundantly across multiple servers, protecting against hardware failure.
Collaboration: Multiple users can work on the same document or project simultaneously in real time.
No maintenance burden: The provider handles hardware maintenance and repairs.
7. Disadvantages of Cloud Computing
Requires Internet: Cloud services are not accessible without a reliable Internet connection.
Security and privacy concerns: Data is stored on third-party servers, raising concerns about privacy and unauthorised access.
Vendor lock-in: Moving data and applications from one cloud provider to another can be difficult.
Costs can grow: While the pay-as-you-go model is cheap initially, heavy usage can lead to large bills.
Limited control: Users have limited control over the underlying infrastructure.
Downtime risk: If the cloud provider faces an outage, all dependent services stop working.
8. Real-World Cloud Services
Some well-known cloud service providers and products include:
Amazon Web Services (AWS): The largest cloud platform, offering EC2, S3 storage, and Lambda services.
Microsoft Azure: Microsoft's cloud platform used by enterprises worldwide.
Google Cloud Platform: Offers Compute Engine, App Engine, and Google Drive.
Google Drive, Dropbox: Popular file storage and sharing services.
Gmail, Office 365: Examples of SaaS email and productivity tools.
GitHub: Cloud-based code hosting and collaboration service.
Cloud computing powers streaming services like Netflix, online gaming, mobile apps, and AI services, proving its importance in every field.
Quick Revision Tables
Service Model
Full Form
What is Provided
Example
IaaS
Infrastructure as a Service
Virtual machines, storage, network
Amazon EC2
PaaS
Platform as a Service
Platform for building apps
Google App Engine
SaaS
Software as a Service
Ready-to-use software
Google Drive
Deployment Model
Ownership
Best For
Public Cloud
Third-party provider
Cost-effective general use
Private Cloud
Single organisation
High security and control
Hybrid Cloud
Public + Private
Balance of cost and security
Community Cloud
Several organisations
Shared common interests
Mind Map
graph TD
A["Cloud Computing"] --> B["Characteristics"]
A --> C["Service Models"]
A --> D["Deployment Models"]
A --> E["Virtualisation"]
A --> F["Advantages"]
A --> G["Disadvantages"]
B --> B1["On-demand, Broad access"]
B --> B2["Pooling, Elasticity, Measured"]
C --> C1["IaaS - Infrastructure"]
C --> C2["PaaS - Platform"]
C --> C3["SaaS - Software"]
D --> D1["Public, Private"]
D --> D2["Hybrid, Community"]
E --> E1["Virtual machines, hypervisor"]
F --> F1["Cost, scalability, accessibility"]
G --> G1["Internet needed, security, lock-in"]
Important Diagrams (SVG)
Diagram 1: Cloud Service Models
Diagram 2: Public vs Private vs Hybrid Cloud
Common Mistakes
Confusing the service models. SaaS is ready software, PaaS is a development platform, and IaaS is raw infrastructure.
Believing that cloud computing requires no Internet connection. Cloud services are completely dependent on the Internet.
Thinking that private cloud is cheaper than public cloud. Private cloud is more expensive due to dedicated infrastructure.
Forgetting that resource pooling and rapid elasticity are essential NIST characteristics of cloud computing.
Confusing virtualisation with cloud computing. Virtualisation is the technology that enables cloud computing, not the same as it.
Assuming that data in the cloud is never lost. Although cloud providers back up data, users should still keep their own backups.
Believing that all cloud services are free. Most are subscription or pay-as-you-go based.
Exam Tips
Learn the full forms and definitions of IaaS, PaaS, and SaaS with one example of each.
Memorise the five characteristics of cloud computing from NIST: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.
Be able to describe public, private, hybrid, and community clouds with an advantage of each.
Remember at least three advantages and three disadvantages of cloud computing for descriptive answers.
Know the definition of virtualisation and its role in cloud computing.
Mention real-world examples such as Google Drive, AWS, and Microsoft Azure to strengthen answers.
Conclusion
Cloud computing has revolutionised how computing resources are delivered and consumed. In this chapter we learned that the cloud provides on-demand, scalable, and measured access to computing resources over the Internet. We studied the three service models, IaaS, PaaS, and SaaS, and the four deployment models, public, private, hybrid, and community clouds. Virtualisation, the enabling technology behind the cloud, allows physical resources to be shared efficiently. While cloud computing offers cost savings, scalability, and accessibility, it also brings challenges of security, vendor lock-in, and Internet dependence. Understanding the cloud prepares students for the modern world of AI services, web development, and data science.