Standards and Concepts · Topic 4 of 6
Cloud and On-Premises Services, SaaS, PaaS and IaaS
Compare cloud and on premises services, learn public, private and hybrid clouds, the SaaS, PaaS and IaaS models, and how remote and hybrid work use them.
- 4 min
- On premises equipment is owned and run by the organisation. Cloud equipment is owned by a provider.
- Public cloud is shared by many customers. Private cloud serves one organisation. Hybrid cloud combines the two.
- IaaS gives you virtual infrastructure. PaaS gives you a platform for your own code. SaaS gives you a finished application.
What it is
Cloud computing means using servers, storage and software that run in someone else's data centre and that you reach over a network.
On premises, often shortened to on prem, means the equipment sits in your own building or data room. You buy it, house it and look after it.
Most organisations use a mix of both. The exam expects you to tell the options apart and say what each one costs you in control and effort.
How it works
The choice depends on who owns the equipment and on how much of the technology stack you manage yourself.
On premises versus cloud
| Point | On premises | Cloud |
|---|---|---|
| Ownership | You own the hardware | The provider owns the hardware |
| Cost style | Large purchase up front | Pay for what you use, usually monthly |
| Growing | Buy and install more equipment | Add capacity quickly |
| Control | Full control over the systems | Less control, you rely on the provider |
| Staff effort | You run and repair everything | The provider runs the hardware |
Neither is always better. A business with strict rules about where data is kept may choose on premises. A business with sudden changes in demand may choose the cloud.
Deployment models
The deployment model says who the cloud is for.
| Model | Who uses it | Example |
|---|---|---|
| Public cloud | Many customers share the provider's infrastructure | A company hosts a website with a large provider |
| Private cloud | One organisation only, in its own or a hosted data centre | A bank runs its own cloud for internal systems |
| Hybrid cloud | A mix of private and public, linked together | Sensitive data stays private while a web front end runs in the public cloud |
Service models
The service model says how much the provider manages for you. The more the provider does, the less you control.
| Model | You get | Provider manages | Example |
|---|---|---|---|
| IaaS, infrastructure as a service | Virtual servers, storage and networks | Physical hardware | A virtual machine you install an operating system on |
| PaaS, platform as a service | A platform to build and run your own applications | Hardware, operating system and runtime | A place to deploy code without managing servers |
| SaaS, software as a service | A finished application | Everything | Web email or an online office suite |
A simple way to remember: with IaaS you rent the building blocks, with PaaS you rent the workshop, and with SaaS you just use the product.
Remote and hybrid work
Remote work means people work from home or another place away from the office. Hybrid work means they split their time between home and the office.
Both rely on the network in several ways. Staff need internet access at home, a secure way to reach company systems, and tools for calls and file sharing. Cloud services help because they can be reached from anywhere with an internet connection.
Companies protect remote staff by using secure connections and by asking for extra proof of identity when they sign in. These ideas appear later in the security chapter.
What to remember for the exam
Six facts cover most questions on this topic.
- On premises equipment is owned and run by the organisation. Cloud equipment is owned by a provider.
- Public cloud is shared by many customers. Private cloud serves one organisation. Hybrid cloud combines the two.
- IaaS gives you virtual infrastructure. PaaS gives you a platform for your own code. SaaS gives you a finished application.
- With SaaS the provider manages the most. With IaaS you manage the most.
- Cloud usually means paying for use, and on premises usually means buying hardware up front.
- Remote and hybrid work depend on network access, security and cloud tools.
Web email is a classic SaaS example. A virtual server you log in to and set up is a classic IaaS example.
Common mistakes
These four errors appear again and again.
Treating private cloud as the same as on premises. A private cloud serves one organisation, but it can be hosted in a provider's data centre.
Mixing up PaaS and SaaS. With PaaS you build your own application. With SaaS you only use an application someone else built.
Assuming the cloud has no hardware. The servers are real, but the provider owns and runs them.
Believing the provider handles everything. In every model, you remain responsible for your own data and for who may access it.
Moving to the cloud does not remove the need for a good network connection. If the internet link fails, cloud services may be out of reach.
Check yourself
Work through these three questions.
A company uses web based email that the provider fully manages. Which service model is this?
This is software as a service, or SaaS.
What makes a cloud hybrid?
A hybrid cloud links a private cloud with a public cloud, so that the two work together.
Why do remote workers need more than an internet connection?
They also need a secure way to reach company systems, and tools for calls and file sharing.
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