The 3 categories are:

•  Infrastructure-as-a-Service (IaaS) - This is the most commonly utilized of the three. It can be a set of storage spaces or bandwidth along with a server or servers within cloud.
• Platform-as-a-Service (PaaS) - A platform which is obviously cloud-based which businesses can utilize to design new apps or create software which works with applications that are already completed or developed.
• Software-as-a-Service (SaaS) - This is cloud's biggest and most established section. Rather than being in a customer's hard disk or in a storage system, SaaS is an app or an array of software which exist within the cloud itself.

 

Similarities:

The three areas are very much distinct from one another, so I only spotted a few similarities among them, and they are as follows:

• The first similarity is that clients pay fees to rent them rather than purchasing them, transforming it from being an investment to being an operational cost.
• Next, everything involved in the operation such as installment, maintenance, administration, planning, tech support, and data recovery are all responsibilities of the providers. A small note to remember, however, is that although providers are accountable for the administration of servers, hard drives, networking, virtualization, and storage, IaaS requires clients to manage applications, runtime, OSes, middleware, and data unlike SaaS and PaaS.
• Both SaaS and PaaS are delivered through the web, while IaaS is delivered via a dashboard or an API.
• Last but not the least, cloud is typically convenient and intuitive to use, including larger storage capacity via an IaaS provider, more PaaS ventures, and perhaps more passes for SaaS clients.

 

 

It is difficult to elaborate all the three points of similarities because they are all self-explanatory already, so I will be providing you with more information about the 3 categories of offering so you can better understand each of them and be able to differentiate from and contrast them with one another as well.

 

Infrastructure as a Service (IaaS)

• Cloud infrastructure services, widely recognized as Infrastructure as a Service (IaaS), are characterized by a highly scalable and advanced compute tools. IaaS is requires an entire self-service to access and manage devices which are mostly computers, networking, storage as well as other forms of services related to it. IaaS helps organizations to invest on services that are on-demand and as-needed rather than needing to purchase hardware entirely.
• IaaS provides infrastructures for cloud computing, involving servers, networks, operating systems and storage, via virtualization. Such cloud servers are usually given to the company through the use of a dashboard or an API, granting IaaS customers full control over every aspect of the infrastructure. IaaS has the same resources and technology as a conventional data center without needing to physically support or handle any of them. IaaS clients can always access their servers and store them directly, however, they're all exported to a "virtual data center" throughout the cloud.
• IaaS clients are given the responsibility to handle factors such as applications, runtime, OSes, middleware, and data, as opposed to SaaS or PaaS. Even so, IaaS providers handle servers, hard disks, networking, virtualization, and storage. Few vendors also offer more features outside the virtualization layer, including databases or queuing of messages.
• Examples of IaaS: DigitalOcean, Linode, Rackspace, Amazon Web Services (AWS), Cisco Metacloud, Microsoft Azure, Google Compute Engine (GCE)

 

 

Platform as a Service (PaaS)

• Cloud platform services, often identified as Platform as a Service (PaaS), offer cloud components to specific software whilst also being utilized primarily for applications. PaaS offers a platform for programmers in which they can develop on and use to build custom applications. Both servers, network and storage can be administered by an entity or a third party vendor, whereas the developers continue to enjoy the privilege to manage the applications.
• The PaaS delivery model is very similar to SaaS, however, instead of distributing software via the Internet, PaaS offers a framework for software development. This framework is distributed through the web, allowing developers to freely focus on developing apps without constantly worrying about the needed operation of systems, software upgrades, storage, or infrastructure. PaaS helps organizations to develop and construct apps which are designed through PaaS including specialized software components. These software, also referred to as middleware, are versatile and widely accessible because they have specific cloud features.
• Examples of PaaS: AWS Elastic Beanstalk, Windows Azure, Heroku, Force.com, Google App Engine, OpenShift

 

 

Software as a Service (SaaS)

• Cloud application services, mostly known as Software as a Service (SaaS), are the representation of the most prominent cloud market and are now continuing to grow rapidly. SaaS utilizes the internet to offer applications which are operated by a third-party provider and its interface is accessible by the customers. In the clients' viewpoints, majority of SaaS apps are designed to be run directly from a browser with no downloads or installations needed, even though some may require plugins.
• Due to the online delivery system, SaaS removes any need to install and run applications on individual devices, specifically computers, which implies that IT personnel is no longer as much needed in this category. Through SaaS, it's convenient for organizations to optimize their maintenance services, since vendors are responsible for everything including the applications, software, runtime, data, middleware, OSes, virtualization, servers, storage and networking.
• SaaS offers several benefits for workers and organizations by dramatically minimizing the resources and time expended on time-consuming activities such as downloading, maintaining and updating software. It saves up a lot of time for technicians to focus on more urgent problems and challenges within the company.
• Examples of SaaS: Google Apps, Salesforce, Workday, Concur, Citrix GoToMeeting, Cisco WebEx

Step-by-step explanation

I did all that I can to acquire details regarding the similarities and everything I included in my guide to your possible answers are all which I found helpful and relevant to the question during my research. All of the information which you can usually find on your research will present the differences and there are almost no results showing the similarities, which justifies why the similarities I have mentioned above are brief yet precise. They are all I have found. I am hoping that through the additional information I gave you about the 3 categories, you acquired more idea about the possible similarities and differences of the 3 categories.