Managed databases versus unmanaged databases
Traditionally, in an on-premises setup, you would configure a server (physical or virtual) with a base operating system and then proceed to install the database software on it. Because the primary purpose of a database is to store data, you would also need to ensure that you had adequate storage attached to your server. Due to the importance of the data store, you would take additional security measures to protect the data and ensure you had adequate backups and copies of the data (ideally stored offsite in another location) in case of disasters.
On AWS, you can set up an Elastic Compute Cloud (EC2) instance and install your database, such as Microsoft SQL Server or Oracle, in the same manner to serve your frontend web and application servers as required. In this case, you take full ownership of managing the database, provisioning the required amount of Elastic Block Store (EBS) volumes for storage, and ensuring adequate backups are made...