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SaaS / IaaS / PaaS

/sæs/ /aɪ ɑːz/ /pæs/noun (acronyms)

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In brief · quick answer

SaaS (Software as a Service), IaaS (Infrastructure as a Service), and PaaS (Platform as a Service) are the three main cloud computing service models. They differ in the level of control and management you have over the computing stack, from fully managed software (SaaS) to virtualized infrastructure (IaaS).

§ 1 Definition

SaaS, IaaS, and PaaS are the three core cloud computing service models that define how businesses consume IT resources. They form a managed-responsibility spectrum: * SaaS (Software as a Service): Ready-to-use software delivered over the internet. The provider manages everything: infrastructure, platform, application, and data. Users just log in and use it. Examples: Google Workspace, Salesforce, Slack. * PaaS (Platform as a Service): A managed platform for developing, deploying, and running applications. The provider manages the underlying infrastructure and runtime. Developers focus on code. Examples: Heroku, Google App Engine, Vercel. * IaaS (Infrastructure as a Service): Virtualized computing resources (servers, storage, networking) delivered on demand. The user manages the operating system, middleware, and applications. Examples: AWS EC2, Google Compute Engine, DigitalOcean.

§ 2 The Managed Responsibility Spectrum

The key difference is what you manage versus what the provider manages: * On-Premises: You manage everything: applications, data, runtime, middleware, OS, virtualization, servers, storage, networking. * IaaS: The provider manages virtualization, servers, storage, and networking. You manage the OS, middleware, runtime, data, and applications. * PaaS: The provider manages everything up to the runtime. You deploy and manage your applications and data. * SaaS: The provider manages everything. You just use the software.

§ 3 Choosing the Right Model

The choice depends on your team, requirements, and risk tolerance: * SaaS is best when you want a turnkey solution with minimal IT overhead. Great for CRM, email, collaboration, and HR tools. You trade customization for convenience. * PaaS suits development teams that want to focus on code without managing servers. Best for web applications and APIs. You get fast deployment but limited infrastructure control. * IaaS provides maximum flexibility. You control the OS, security, and scaling. Suitable for complex migrations, custom infrastructure, or when compliance requires specific configurations.

§ 4 The XaaS Ecosystem

Beyond the three core models, the "as a service" model has expanded to nearly every IT domain: FaaS (Functions as a Service) for serverless computing, DBaaS (Database as a Service) for managed databases, MaaS (Monitoring as a Service) for observability, and DaaS (Desktop as a Service) for virtual desktops. The unifying theme is outsourcing operational complexity in exchange for a predictable subscription cost. The tradeoff is always control versus convenience. Know what you are giving up before you subscribe.

§ 5 Common questions

Q. Which model is cheapest?: A. SaaS has the lowest upfront cost (subscription only). IaaS can be cheaper at scale but requires more operational expertise. PaaS sits in the middle. The true cost depends on your team size and operational efficiency.
Q. Can I use all three models together?: A. Yes, and many organizations do. A company might use SaaS for email (Google Workspace), PaaS for web apps (Heroku), and IaaS for data processing (AWS EC2). This is called a hybrid or multi-cloud strategy.
Q. Is serverless the same as PaaS?: A. Serverless (FaaS) is a subset of PaaS but with even finer granularity. PaaS charges for allocated resources; serverless charges for actual execution time. Both abstract away infrastructure management.

Key takeaways

SaaS, PaaS, and IaaS differ in the level of control versus convenience across the computing stack.
SaaS = fully managed software. PaaS = managed platform for building apps. IaaS = virtualized infrastructure.
Choose based on your team's operational capacity and customization requirements.
The as-a-service model has expanded to FaaS, DBaaS, DaaS, and many more specialized offerings.

How Atomic Glue helps

We help clients navigate the cloud model landscape. From selecting the right SaaS tools to architecting PaaS or IaaS deployments, we match the model to the need. Get in touch.

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# SaaS / IaaS / PaaS

Category: General (also: Software Engineering, Infrastructure)

Author: Atomic Glue Technical Team

## Definition

SaaS, IaaS, and PaaS are the three core cloud computing service models that define how businesses consume IT resources. They form a managed-responsibility spectrum: * **SaaS (Software as a Service):** Ready-to-use software delivered over the internet. The provider manages everything: infrastructure, platform, application, and data. Users just log in and use it. Examples: Google Workspace, Salesforce, Slack. * **PaaS (Platform as a Service):** A managed platform for developing, deploying, and running applications. The provider manages the underlying infrastructure and runtime. Developers focus on code. Examples: Heroku, Google App Engine, Vercel. * **IaaS (Infrastructure as a Service):** Virtualized computing resources (servers, storage, networking) delivered on demand. The user manages the operating system, middleware, and applications. Examples: AWS EC2, Google Compute Engine, DigitalOcean.

## The Managed Responsibility Spectrum

The key difference is what you manage versus what the provider manages: * **On-Premises:** You manage everything: applications, data, runtime, middleware, OS, virtualization, servers, storage, networking. * **IaaS:** The provider manages virtualization, servers, storage, and networking. You manage the OS, middleware, runtime, data, and applications. * **PaaS:** The provider manages everything up to the runtime. You deploy and manage your applications and data. * **SaaS:** The provider manages everything. You just use the software.

## Choosing the Right Model

The choice depends on your team, requirements, and risk tolerance: * **SaaS** is best when you want a turnkey solution with minimal IT overhead. Great for CRM, email, collaboration, and HR tools. You trade customization for convenience. * **PaaS** suits development teams that want to focus on code without managing servers. Best for web applications and APIs. You get fast deployment but limited infrastructure control. * **IaaS** provides maximum flexibility. You control the OS, security, and scaling. Suitable for complex migrations, custom infrastructure, or when compliance requires specific configurations.

## The XaaS Ecosystem

## Common questions

Q: Which model is cheapest?

A: SaaS has the lowest upfront cost (subscription only). IaaS can be cheaper at scale but requires more operational expertise. PaaS sits in the middle. The true cost depends on your team size and operational efficiency.

Q: Can I use all three models together?

A: Yes, and many organizations do. A company might use SaaS for email (Google Workspace), PaaS for web apps (Heroku), and IaaS for data processing (AWS EC2). This is called a hybrid or multi-cloud strategy.

Q: Is serverless the same as PaaS?

A: Serverless (FaaS) is a subset of PaaS but with even finer granularity. PaaS charges for allocated resources; serverless charges for actual execution time. Both abstract away infrastructure management.

## Key takeaways

SaaS, PaaS, and IaaS differ in the level of control versus convenience across the computing stack.
SaaS = fully managed software. PaaS = managed platform for building apps. IaaS = virtualized infrastructure.
Choose based on your team's operational capacity and customization requirements.
The as-a-service model has expanded to FaaS, DBaaS, DaaS, and many more specialized offerings.

## Related entries

Last updated July 2025. Permalink: atomicglue.co/glossary/saas