Depends how a Removable Hard Drive is connected to a desktop or laptop.
As a general rule, SATA and PATA IDE drives are seen as Integrated Devices, whereas a USB or IEEE 1394 device are seen as Removable devices.
If you are looking in the BIOS, many time they will be recognized as IDE devices on the CMOS page. If you have an external device connected at bootup, it will be there also.
Might relate exactly what external HDD you have, how it is cable connected, and how you and the Operating System are recognizing it.