This whitepaper from the ArcGIS Enterprise product management team, discusses the two ways data can be handled with the ArcGIS Platform:
User Managed: where data owners and admins are responsible for providing and managing the underlying storage infrastructure, e.g., file servers and database servers.
ArcGIS Managed: the concept of hosted data because the data is stored within (hosted by) the ArcGIS system and exposed solely through REST based web services that are shown to end users as layer items within their portal.
Also for ArcGIS Enterprise users, the ArcGIS Data Store is not a replacement for existing enterprise geodatabases. .
Great whitepaper by Shannon Kalisky that provides a technical overview of ArcGIS Enterprise, its software components, key concepts such as federation, and outlines 3 options for completing a migration from a standalone ArcGIS Server deployment to the standard configuration of ArcGIS Enterprise called the base ArcGIS Enterprise deployment. It includes an outline of the key benefits, high-level steps, and important considerations for each migration option.
FYI, several users requested a copy of this Esri UC 2017 technical workshop:
ArcGIS Enterprise: Managing ArcGIS Server
ArcGIS Server is the component of ArcGIS Enterprise that enables you to take your GIS resources such as maps and models, and share them as web services. Publishing your GIS resources as web services enables them to be used throughout the ArcGIS platform. This presentation will examine ArcGIS Server at a deeper technical level. Attendees will learn how to administer an ArcGIS Server site more effectively. Topics include: security, defining data stores, log files, and working with the Server Administrator directory.
FYI: at the 10.5 release, the product "ArcGIS for Server", has been renamed to "ArcGIS Enterprise". The product was re-branded to better reflect the idea that with the software you get "Web GIS" in your own infrastructure. Learn more here.