The differences between the three primary service models of cloud computing – Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS) – can be understood in terms of what each model offers and manages for the user:

1. Infrastructure as a Service (IaaS)

• What it offers: IaaS provides virtualized computing resources over the internet. In an IaaS model, a cloud provider hosts the infrastructure components traditionally present in an on-premises data center, including servers, storage, and networking hardware, as well as the virtualization or hypervisor layer.
• User Control: The user manages the operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls).
• Use Cases: Suitable for organizations looking to avoid the cost and complexity of purchasing and managing physical servers and data center infrastructure. Each resource is offered as a separate service component, and you only need to rent a particular one for as long as you need it.
• Examples: Amazon Web Services (AWS) EC2, Microsoft Azure Virtual Machines, Google Compute Engine.

1. Platform as a Service (PaaS)

• What it offers: PaaS provides a platform allowing customers to develop, run, and manage applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app.
• User Control: Users manage the applications and services they develop, and the cloud provider typically manages everything else, like the operating system, middleware, and hardware.
• Use Cases: Ideal for developers who want to create applications without spending time on configuring and managing servers, storage, network, and database.
• Examples: Google App Engine, Microsoft Azure App Services, AWS Elastic Beanstalk.

1. Software as a Service (SaaS)

• What it offers: SaaS provides a completed product that is run and managed by the service provider. In most cases, people referring to Software as a Service are referring to end-user applications.
• User Control: With a SaaS offering, you do not have to think about how the service is maintained or how the underlying infrastructure is managed; you only need to think about how you will use that particular piece software.
• Use Cases: Suitable for services that demand minimal customization and are widely used, such as email services, customer relationship management (CRM) software, and collaboration tools.
• Examples: Google Workspace, Microsoft Office 365, Salesforce.

In summary:

• IaaS: Provides the building blocks for cloud IT and typically provides networking features, computers (virtual or on dedicated hardware), and data storage space.
• PaaS: Provides a platform allowing customers to develop, run, and manage applications without the complexity of building the infrastructure.
• SaaS: Provides a software application over the internet, on-demand and typically on a subscription basis, with the cloud provider managing all potential technical issues like data, servers, and storage.