Exchange
All the issues described earlier in this section apply to a comparison of Exchange Online with the on-premises version of Exchange. An Exchange Server deployment can be an elaborate and expensive affair requiring multiple servers and extensive configuration, while administrators can have Exchange Online up and running in less than a day.

Exchange Online provides each user with 50 or 100 GB of storage. In an on-premises exchange installation, the size of users’ mailboxes is regulated by the administrators, who often do not want to expend that much storage space, which many users might never need.

Also, unlike Exchange Server, Exchange Online can create Microsoft 365 groups, enabling users to work with shared resources. This can be a valuable resource for administrators. For example, a technical support team can add its members to a Microsoft 365 group. Administrators then grant the group the permissions necessary to access a shared Exchange mailbox, a SharePoint team site, and other resources. When members enter or leave the group, the permissions to access those resources are automatically granted or revoked.

On Exchange Server, by default, user mailboxes exist on one server and are therefore vulnerable to hardware failures, system faults, and other disasters that can render them temporarily unavailable or even lead to data loss. For this reason, an enterprise exchange deployment often requires additional servers to maintain duplicate mailboxes, a reliable backup strategy, and in some cases, duplicate datacenters, all of which add to the cost of the installation. By default, Exchange Online replicates mailbox databases across servers and datacenters, ensuring the continuous availability of the service. This, too, is an issue that some Exchange administrators would prefer to address themselves rather than leave to a service provider, but the market for organizations that like the idea of a turnkey solution and are willing to trust cloud services is growing constantly.
Note Hybrid Service Deployments
Another possible solution to the availability issues inherent in on-premises Exchange, SharePoint, and Active Directory implementations is for an organization to create a hybrid service deployment using on-premises servers and cloud services together. The cloud service can therefore function as an availability mechanism that might be more economical than creating redundant on-premises servers or datacenters. When you replicate mailboxes, sites, or AD accounts to the cloud, they can take advantage of Microsoft΄s security mechanisms. A hybrid deployment can also function as a migration mechanism for organizations that want to move from on-premises services to cloud-based ones gradually.

The full pre study guide is at: https://www.acedexam.com/ms-900-microsoft-365-fundamentals/

SharePoint
As with Exchange, SharePoint is available as an on-premises server product and as a cloud-based SharePoint service. The main advantages of the cloud version are the same as those of the other services: simplified deployment, automatic updating, data redundancy, web-based administration, and so forth.

Microsoft is presenting its cloud-based products as the next wave in business computing, and SharePoint in Microsoft 365 is now the flagship of the venerable SharePoint product. New features like the Modern experience in site design appear in the cloud version of SharePoint first. However, in the case of SharePoint, this does not mean that SharePoint Server is being left behind.

SharePoint Server 2019 includes features enabling it to work with Microsoft 365 cloud services. For example, administrators can redirect the MySites link in SharePoint Server to OneDrive so that users will be directed to cloud storage rather than to the on-premises server. A hybrid cloud search capability also causes a Microsoft 365 search to incorporate the index from an on-premises server into the standard cloud search.