In this post I will slightly explain the Build Controller and the Build Agent.
The following is step-by-step video for the post.
Build Service is a Windows Service that can only has one Build Controller, configured for only one Team Project Collection and has multiple Build Agents as needed, of course there is a workaround to have multiple Build Controller on the same machine but this is not recommended in production environment, for more info see, Configuring Multiple TFS Build Controller on the Same Machine. 
Only one Build Controller can exist on the same machine, we can have Build Controller running with the TFS AT (Team Foundation Server Application Tier) but the Build Agent not recommended to be exist on the TFS AT, this because the Build Agent doing intensive work and we don’t want to slow down our TFS AT.
Example of Build Server that has one Build Controller, configured for one Project Collection and has multiple Build Agents.
Removing the build configuration so we can reconfigure and see the number of recommended Build Agents and the Windows Service.
If the Build is not configured we can see that there is no Windows Service.
The Windows Service for the build exist if the build is configured (Registered).
When the processor is (1) processor, the available Build Agent is (2) and the recommended is (1).
When the processor is (4) processor, the available Build Agent is (8) and the recommended is (1).
Links:
Great article & video .. keep it up!
Thanks!