Aqui esta un poco de información:
http://segaretro.org/Master_System_Floppy_Disk_DriveMaster System Floppy Disk Drive
Made by: Sega
Made For: Sega Master System
The Sega Master System Floppy Disk Drive is an unreleased peripheral for the Sega Master System. It seems that at one point, as well as being able to run cartridges and Sega Cards, Sega had planned for their console to be able to run 3.5-inch floppy disks. It can be seen as a spiritual successor to the Super Control Station SF-7000.
The floppy disk drive would have been attached underneath the Master System console (Power Base), similar to the original Sega Mega CD. Little else is known about the peripheral, and we do not know if a Sega Mark III version was planned. It is likely that cost played a large part in the cancellation of this accessory - in 1986 3.5-inch floppy disks were still expensive to produce (at least in comparison to other media formats).
Sega would plan a floppy disk drive for the Sega Mega Drive too, though again this would not be released, however a floppy disk drive for the Sega Saturn would eventually see a release in Japan.