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Cloud computing is the delivery of computing resources such as servers, storage, databases, networking, software and analytics over a network on demand. Instead of purchasing and operating every system entirely in its own data centre, an organisation can consume technology as a service and scale it according to need.
Cloud computing underpins services from Microsoft 365 and Salesforce to Microsoft Azure, Amazon Web Services and modern AI platforms. Understanding the basic service and deployment models is useful not only for technical staff but also for managers, project professionals and anyone involved in digital transformation.
What is cloud computing in simple terms?
Traditional IT often required an organisation to purchase servers, install them in a data centre, provide power and cooling, install operating systems, maintain hardware and plan capacity years ahead.
Cloud computing changes the consumption model. A provider operates large-scale infrastructure and makes computing capabilities available as services.
A business can therefore provision resources when needed, use them over a network and pay according to the provider's pricing model rather than owning every underlying component.
The five characteristics of cloud computing
The widely used NIST definition identifies five essential characteristics of cloud computing.
On-demand self-service
Customers can provision computing capabilities when required without waiting for a provider employee to perform every routine action manually.
Broad network access
Cloud capabilities are available across networks and can be accessed through standard mechanisms from suitable client devices and systems.
Resource pooling
Providers pool computing resources to serve multiple customers, allocating resources dynamically according to demand while maintaining appropriate separation.
Rapid elasticity
Resources can often scale up or down quickly. This means an organisation does not have to purchase hardware for the maximum demand it might experience several years in the future.
Measured service
Cloud platforms meter resource use. Consumption can be monitored, controlled and reported, forming the basis for usage-based or subscription pricing models.
What are IaaS, PaaS and SaaS?
The three classic cloud service models are:
- IaaS - Infrastructure as a Service
- PaaS - Platform as a Service
- SaaS - Software as a Service
The main difference is how much of the technology stack the provider manages on the customer's behalf.
What is Infrastructure as a Service?
IaaS provides fundamental computing resources such as virtual machines, storage and networking.
The cloud provider manages the physical data centre, hardware and virtualisation platform. The customer retains more responsibility for what runs on top, such as:
- operating systems
- applications
- data
- many security configurations
- some network controls
A virtual server running in Azure or AWS is a common IaaS example.
When is IaaS useful?
IaaS is useful when an organisation wants cloud scalability but still needs significant control over operating systems and applications.
Typical scenarios include:
- hosting existing applications on virtual machines
- creating development and test environments
- running specialised server software
- disaster recovery
- extending on-premises infrastructure into the cloud
What is Platform as a Service?
PaaS provides a managed application platform.
The provider manages more of the underlying infrastructure and operating environment, allowing developers to concentrate on applications and data.
PaaS examples can include:
- managed application hosting
- managed databases
- integration services
- application runtimes
- serverless development platforms
The exact boundary varies between services, but the principle is that the customer manages less infrastructure than with IaaS.
Why do developers use PaaS?
PaaS can reduce time spent installing operating systems, patching servers and maintaining supporting infrastructure.
This allows development teams to focus more heavily on application code, configuration, data and user requirements.
What is Software as a Service?
SaaS provides a complete application that users consume as a service.
The provider operates the underlying infrastructure and application platform, while the customer normally manages areas such as users, data, permissions and application configuration.
Common SaaS examples include:
- Microsoft 365
- cloud CRM systems
- online accounting software
- web-based collaboration tools
- cloud service desks
Users typically access SaaS through a browser, mobile application or client software rather than managing servers themselves.
IaaS vs PaaS vs SaaS
| Model | What you receive | Customer control | Typical users |
|---|---|---|---|
| IaaS | Virtual infrastructure | High | Infrastructure teams, administrators |
| PaaS | Managed application platform | Medium | Developers, application teams |
| SaaS | Complete application | Lower technical control | Business users, application administrators |
“Less control” does not mean less responsibility. Customers still need to manage identities, data, permissions, configuration, compliance and appropriate use according to the service involved.
What is the shared responsibility model?
Cloud security is shared between the provider and customer.
The provider is responsible for areas such as physical data centres and the infrastructure components included in the service. The customer remains responsible for areas that depend on how the service is configured and used.
The balance changes according to the service model.
With IaaS, the customer manages more layers.
With SaaS, the provider manages more of the technical stack, but the customer still needs to manage users, information and configuration appropriately.
What are the main benefits of cloud computing?
Faster provisioning
Infrastructure that once required purchasing and installing hardware can often be created in minutes.
Scalability
Resources can be expanded or reduced in response to workload demand.
Global reach
Major providers operate regions around the world, allowing organisations to deploy services closer to customers and users where appropriate.
Reduced capital expenditure
Cloud services can reduce the need for large upfront hardware purchases, although cost management remains essential.
Access to advanced services
Cloud platforms provide services for databases, analytics, AI, integration, security, containers and many other technologies that would be complex to build independently.
Resilience options
Cloud platforms offer multiple availability and disaster-recovery architectures, although resilience must still be designed deliberately.
What are the risks of cloud computing?
Cloud adoption also introduces risks and responsibilities.
These can include:
- poorly controlled costs
- misconfigured security
- overly broad permissions
- data location or compliance concerns
- dependency on network connectivity
- provider or region outages
- vendor lock-in
- skills gaps
- complexity across cloud and on-premises systems
Moving a poorly designed application to the cloud does not automatically make it secure, resilient or inexpensive.
Public, private and hybrid cloud
Cloud service models describe what kind of service is consumed. Deployment models describe how the cloud environment is provided.
The main terms include:
- public cloud
- private cloud
- hybrid cloud
Many organisations combine cloud platforms with existing data centres and specialist environments.
See Public vs Private vs Hybrid Cloud for a detailed comparison.
What is public cloud?
Public cloud services are provided by a third-party cloud provider using shared large-scale infrastructure.
Major examples include:
- Amazon Web Services
- Microsoft Azure
- Google Cloud
Customers receive logically isolated services while the underlying provider infrastructure serves many organisations.
What is private cloud?
A private cloud environment is dedicated to one organisation.
It may be located in the organisation's own data centre or operated by a third party. The important point is that the cloud infrastructure is dedicated to that organisation rather than offered as a general shared public cloud service.
What is hybrid cloud?
Hybrid cloud combines cloud environments with on-premises or private infrastructure in an integrated architecture.
An organisation might keep some workloads in its own data centre while using Azure or AWS for other applications, backup, analytics or burst capacity.
Cloud computing vs traditional data centres
Cloud does not eliminate data centres. It changes who operates them and how customers consume the resources.
Public cloud providers run enormous physical data centre estates. Many businesses also retain their own facilities or colocation environments for workloads that are not appropriate to move.
The result is often a mixed infrastructure rather than an instant replacement of everything on premises.
What is virtualisation?
Virtualisation allows physical computing resources to support multiple logical environments.
It was an important enabler of cloud computing because it made infrastructure more flexible and easier to pool and allocate.
Modern cloud platforms also rely heavily on containers, software-defined networking, automation and distributed systems.
What is serverless computing?
Serverless computing allows developers to run code or consume services without managing the underlying servers directly.
There are still servers in the provider's data centre. “Serverless” means that the customer does not provision and manage those servers in the traditional way.
Serverless models can be especially useful for event-driven applications and variable workloads.
What are cloud regions and availability zones?
Major cloud providers divide infrastructure geographically.
A region represents a geographic area containing provider infrastructure.
Availability-zone concepts divide regions into physically separated locations designed to help customers build resilient solutions.
The exact architecture and terminology differ between providers, so cloud designs should follow the current guidance for the chosen platform.
AWS vs Azure
AWS and Microsoft Azure both provide broad public-cloud platforms.
The better learning route usually depends on the technologies used by your organisation and the roles you want to perform.
See AWS vs Azure Certification: Which Cloud Path Should You Choose?.
How should beginners learn cloud computing?
A sensible progression is:
- Understand cloud characteristics and service models.
- Learn the difference between public, private and hybrid cloud.
- Understand regions, availability and shared responsibility.
- Choose one major platform for practical learning.
- Learn identity, networking, compute and storage fundamentals.
- Practise cost awareness and security.
- Build small cloud resources rather than relying only on theory.
- Progress towards administration, architecture, development, security or data according to your role.
Frequently asked questions
Is Microsoft 365 cloud computing?
Yes. Microsoft 365 is primarily delivered as Software as a Service.
Is Azure IaaS or PaaS?
Azure provides IaaS, PaaS and other cloud service models. Individual services have different responsibility boundaries.
Is AWS the cloud?
AWS is one major public cloud provider. Cloud computing is the broader technology and service model.
Do cloud services always save money?
No. Cloud can reduce capital expenditure and improve flexibility, but poorly managed resources can become expensive. Cost governance and architecture remain important.
Is cloud computing secure?
Cloud platforms can support strong security, but security depends on both provider controls and correct customer configuration, identity management, data protection and governance.
Do I need programming skills to learn cloud computing?
Not for every role. Cloud administrators and architects benefit from scripting and automation, while introductory cloud and business roles can begin without programming.
Develop your cloud skills with ExperTrain
ExperTrain offers instructor-led AWS training and Microsoft Technical training covering cloud fundamentals through administration, architecture, development, security and data.
Beginners can start with AWS Cloud Practitioner Essentials or Microsoft Azure Fundamentals (AZ-900).
You can also explore the AWS Glossary and Microsoft Azure Glossary for key cloud terminology.
Further reading
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