An administrator is upgrading an ESXi 5.5 host to ESXi 6.x and gets the following error: MEMORY_SIZE What does this indicate?

ESXi 6.x requires a minimum of 4 GB of physical RAM, compared to 2 GB for ESXi 5.5. When the installer detects that the host's installed memory falls below this threshold, it halts with a MEMORY_SIZE hardware compatibility error, blocking the upgrade on that specific host.

Auto Deploy is a stateless provisioning feature that PXE-boots ESXi images; it does not perform prerequisite memory checks on target hosts that would surface as a MEMORY_SIZE error.

vCenter Server runs on its own separate appliance or VM with independent memory requirements; the MEMORY_SIZE error originates from the hardware validation check on the ESXi host being upgraded, not on vCenter.

Update Manager orchestrates the upgrade workflow but the MEMORY_SIZE error is generated by the ESXi installer binary validating hardware requirements on the target host, not by Update Manager itself.