I haven't touched one since 1992-93, so my memory is fuzzy. As stated the 181 didn't support an internal hard drive. The 183 with the hdd option had an hdd with a controller connected with a ribbon cable, and the controller board was sandwiched to the main board. A screw and a spacer held it in place. If the screw came loose, the controller could unseat from the main board. Without opening it, you can tell if it had a hard drive or not because the second floppy drive pops out of the area a hard drive would sit. Otherwise you'll have to open it up to verify the controller didn't pop off it's connector.Does anyone know if there is a way to tell if the HDD controller is installed without opening the machine up?