The "Penthouse Expansion System" is an expansion box that mounts on top of the Tandy 1000EX and 1000HX computers. It adds an additional drive and provides space for two extra Plus cards.

Depending upon the model, the drive could be a 1.44MB 3.5" floppy, CD-ROM, or hard disk. The floppy version appeared in the 1994 "PC Enterprises" catalog for $239 dollars, as item number 13215.

The EX and HX came with the older 360K 5.25" or 720K 3.5" drives and controllers, so the ability to read CD-ROMs or 1.44MB disks enables them to access more recent software and data.