Many Modern CPC users replace their old 3" by an external 3"1/2, often adding a Disk drive A-B / B-A switcher (allowing to use the external disk Drive as if it were the internal one = Drive A). Also and/or a side switcher allows to allow to use a 3"1/2 disk like a 3" disk... switching manually the sides as needed by good old 3" disk drives (yet a decent sofware can do it).
The side switcher and A-B drive's switchers are needed only if you use old softwares, as most of them couldn't really figure they were loaded from B drivers, or has no such feature as double sided drives.
They were designed for good old 3" drive so the 720 720Ko DD extgernal 3"1/2 is not implemented.
But modern softwares designers can allow this fairly more easily.
It is to the CPC-scene to design their softwares to include thoseoptions, allowing more un-modded drives to be simply used as external B drives with no need to add extra buttons and cable montages on the Amstrad. As modifying all the software library of the good gay old time seems impractical, yet modern era software have to use this.
== Softwares released on 3"1/2 disk==