Cloud Models and Definitions Review infographic showing IaaS, PaaS, SaaS, deployment models and NIST cloud computing characteristics

Cloud Models & Definitions Review – IaaS PaaS SaaS Explained

Cloud computing has reshaped modern IT. Instead of buying physical servers and maintaining them on-site, organizations can access computing power, storage, and software through the internet—often within minutes. If you’re studying for an exam or building your foundation in tech, the fastest path is to master the cloud models and the most common cloud definitions. This review breaks everything down in a clear, reader-friendly way.

What is Cloud Computing?

Cloud computing is a service-oriented approach that delivers computing resources—such as servers, storage, databases, networking, and applications—over the internet. Instead of owning infrastructure, users access resources when needed, scale up or down depending on demand, and pay based on usage.

This model is popular because it supports:

  • Speed: deploy resources quickly without waiting for physical setup
  • Cost efficiency: reduce upfront hardware purchases and maintenance
  • Scalability: handle traffic spikes with elastic resources
  • Accessibility: manage systems from anywhere with network access
  • Reliability: distribute workloads across multiple resources

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Cloud Service Models (IaaS, PaaS, SaaS)

Cloud service models describe how much the provider manages versus how much you manage. The more you move from IaaS to SaaS, the more the provider handles for you.

Infrastructure as a Service (IaaS)

IaaS provides virtual infrastructure: compute (VMs), storage, and networking. The provider manages physical hardware and virtualization, while you manage the operating system and everything installed on top of it.

  • You manage: OS, applications, middleware, runtime, data
  • Provider manages: servers, storage hardware, networking equipment, virtualization

Examples: AWS EC2, Azure Virtual Machines, Google Compute Engine.

Platform as a Service (PaaS)

PaaS provides a managed platform for building and deploying applications. It includes runtime environments, middleware, scaling support, and developer tools, so teams can focus on coding instead of server administration.

  • You manage: your app code and data
  • Provider manages: runtime, OS, infrastructure, scaling, platform services

Examples: Google App Engine, Heroku, Azure App Service.

Software as a Service (SaaS)

SaaS delivers complete applications over the internet. You log in and use the software immediately—no installation, no manual updates. Maintenance, security patches, and uptime are handled by the provider.

  • You manage: user access, permissions, account security, content
  • Provider manages: the app, infrastructure, availability, updates

Examples: Microsoft 365, Google Workspace, Salesforce.

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Cloud Deployment Models

Public Cloud

Public cloud services are delivered over the internet and shared across multiple customers. It’s popular because it is scalable and cost-effective.

Private Cloud

Private cloud infrastructure is dedicated to a single organization. It offers more control, customization, and may be preferred for strict compliance requirements.

Hybrid Cloud

Hybrid cloud combines public and private environments (and sometimes on-premise). It’s useful when some workloads must stay private while others need public-cloud scalability.

Key Cloud Definitions You Must Know

Multi-tenancy

Multiple customers share the same cloud infrastructure while remaining securely isolated. This drives efficiency and helps reduce costs.

Elasticity

The ability to scale resources up or down so capacity matches demand. This improves performance during spikes and saves cost during low usage.

On-demand self-service

Users can provision computing resources automatically (like deploying a VM or increasing storage) without provider support.

Resource pooling

Cloud providers pool physical and virtual resources, then allocate them dynamically to customers based on demand.

Middleware

Software that connects applications or services so they can communicate—common in enterprise systems and cloud-native environments.

Load balancing

Distributes traffic across multiple servers to avoid downtime and prevent any single server from becoming a point of failure.

DevOps

A set of practices that improves collaboration between development and operations. DevOps often includes CI/CD pipelines, automation, monitoring, and infrastructure as code—especially important in cloud environments.

NIST Essential Characteristics

Cloud computing is commonly identified using the NIST essentials:

  • On-demand self-service
  • Broad network access
  • Resource pooling
  • Rapid elasticity
  • Measured service

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FAQ

What are the three main cloud service models?

Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS).

What is the difference between IaaS and PaaS?

IaaS provides infrastructure (VMs, storage, networking), while PaaS provides a managed platform with runtime and tools so developers can build and deploy apps without managing servers.

Why is SaaS popular?

SaaS is popular because users can access software through a browser without installing, updating, or maintaining it locally.

What are the NIST essential characteristics of cloud computing?

On-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service.

Final Thoughts

Once you understand IaaS, PaaS, and SaaS, cloud computing becomes much easier to learn. Combine that with deployment models (public, private, hybrid) and the essential definitions like elasticity and multi-tenancy, and you’ll be ready for exams and real-world cloud platforms.