Managed and Standalone ESX/ESXi Hosts
You can run ESX/ESXi as a managed or standalone ESX/ESXi host.
Standalone ESX/ESXi hosts are standalone hosts with limited capabilities. The inventory of a standalone host can support multiple virtual machines and multiple resource pools, but it contains a single default datacenter and a single root folder. The default datacenter and root folder are not visible in the vSphere Client, but they exist in the inventory of a standalone host and they are visible in the MOB.
Managed ESX/ESXi hosts have been added to the vCenter Server inventory. Available features depend on the licenses available for that host. For example, you can configure two or more hosts for VMware DRS resource management or VMware HA failover protection.
Standalone ESX/ESXi and vCenter Server Inventories summarizes the differences between the number of objects that an inventory can contain. See also ESXi Inventory Hierarchy and vCenter Server Inventory Hierarchy.