Clarifying terms -
This is an extended storage phone.
Its built-in storage includes the Android-standard /sdcard folder that any Android app can access.
In the past, that was a separate part that the user could plug and unplug. Not so on extended storage phones.
This is the only One X model that also includes a micro sd card socket. When a user plugs a card in there, it is known to the user, and any advanced apps that understand this scheme, as /sdcard2.
For convenience, it's also known by the shortcut, /sdcard/ext_sd.
For the Linux-savvy, the actual system mount points are found under /mnt, let's leave that discussion reserved for the root forum. The sdcard0 and sdcard1 monikers are also accurate, but better used in root discussions as well.
Hope this helps!