The blue-colored areas in the diagram are the user's; the orange-colored areas show the layers that are under the responsibility of the contractor firm. The four concepts you see in the image; It shows four different types of service.
On-Premises is the classic method of installing its own data center, which has been used for years; and managing all the resources you put in it. From network connections to servers, from virtualization to the application itself, it seems that all responsibility belongs to the user.
Infrastructure as a Service, that is, the provision of infrastructure as a service. It is a service model in which virtual machine and network structures are made by the user by taking service over the data center established by another company.
Platform as a Service is the name given to the application that the user will run only on the platform and the method to be managed through this application, responsible for the management of the entire infrastructure, including the management of the servers of the serving company. Thanks to this service, software teams can put the application they have created on the cloud service and run it from there without the hassle of managing the services running in the infrastructure.
Software as a Service, the entire responsibility of the entire infrastructure and application of this concept lies with the company that receives the service. You can only benefit from this service by paying the fee.