Proface PS4800 - 19 Panel PC" - Manual (Page 33)

Physical Overview
33
12 Slide in Slot 2 (Connection via SATA)
NOTE: The front USB is a diagnostic interface for service and maintenance.
NOTICE
UNINTENDED EQUIPMENT OPERATION
・Do not use the front USB (USB5) while the machine is in operation.
・Always keep the blue cover closed during normal operation.
Failure to follow these instructions can result in equipment damage.