Cloud computing is the delivery of computing resources over a network as a service. Instead of owning all the physical servers, storage, networking, and software locally, a user or organisation can rent access to shared resources from a provider and scale that use as needed.
The National Institute of Standards and Technology defines cloud computing as on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or provider interaction. That definition is still widely used because it separates cloud computing from ordinary remote hosting.
Core Characteristics
NIST describes five essential characteristics:
- On-demand self-service, where customers can provision resources without manual contact for each request.
- Broad network access, where services are available over a network through standard mechanisms.
- Resource pooling, where provider resources serve multiple customers while keeping workloads logically separated.
- Rapid elasticity, where capacity can scale up or down quickly.
- Measured service, where usage can be monitored, controlled, reported, and billed.
These characteristics are why cloud services can feel flexible compared with buying physical equipment in advance.
Service Models
Cloud services are commonly grouped into three main service models:
Infrastructure as a Service
Infrastructure as a Service provides virtual machines, storage, networks, firewalls, load balancing, and related infrastructure. The customer usually controls the operating system and applications, while the provider runs the underlying facilities and hardware.
Platform as a Service
Platform as a Service gives developers a managed environment for applications. The provider handles more of the runtime, scaling, database, or deployment layer. The customer focuses more on the application code and configuration.
Software as a Service
Software as a Service provides a complete application over the network. Users access the software through a browser, app, or client without managing the servers that run it. Email, document collaboration, customer-management systems, and support desks are common examples.
Deployment Models
NIST also describes four deployment models:
- Public cloud, where infrastructure is offered for use by the public or a broad customer base.
- Private cloud, where cloud infrastructure is used by one organisation.
- Community cloud, where infrastructure is shared by organisations with common needs.
- Hybrid cloud, where separate cloud environments are connected in a way that allows data or workloads to move between them.
In practice, many organisations use a mixture of public cloud, private systems, hosted servers, and on-site equipment.
Advantages
Cloud computing can reduce the need to buy hardware before demand is known. It can make testing, deployment, backup, disaster recovery, and global distribution faster. It can also give smaller teams access to infrastructure that would previously have required a larger operations department.
Cloud platforms can provide managed databases, queues, monitoring, identity tools, security services, content delivery, machine-learning tools, and automation. These services can speed up delivery, but they also increase dependence on the provider's platform and pricing model.
Risks and Limitations
Cloud computing does not remove responsibility from the customer. Access control, data classification, backups, software security, logging, compliance, and cost management still matter.
Common risks include:
- Misconfigured storage, identity, or network rules.
- Unexpected bills caused by traffic, storage growth, or inefficient design.
- Vendor lock-in, where services are hard to move elsewhere.
- Outages affecting services in one provider or region.
- Data residency and compliance issues.
- Weak monitoring that hides failures until users notice them.
The best cloud design treats the provider as a powerful tool, not as a substitute for engineering judgement.
Data Centres
Cloud computing depends on large data centres connected by high-capacity networks. Users may not see the physical hardware, but the service still depends on buildings, power, cooling, fibre routes, spare parts, technicians, security, and operational discipline.
The growth of cloud and AI services has increased public attention on electricity demand, water use, resilience, and planning around data-centre sites.
See Also
References
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