So, and here's a candypiece for those who haven't seen it yet. It's an original HDI, that is, the interface for connecting up to 4 standard drives to the XL/XE. Here you can mix 3,5" and 5,25" floppies at will. Required is that the drive supports the Disk Change signal at pin 34 of the Shugart bus. It doesn't support Medium Density (128 bytes/sector in MFM mode and 1.2 MB drives). Maximum transfer rate: 500 Kbit/s (1.44 MByte disks). The HDI is sold out.