Mounting external floppy drive in Mavericks

Have you tried unplugging and plugging back in the USB drive?

Does the external floppy drive have driver software that needs to be updated or installed with a Mavericks compatible version?

If the disk drive shows up in Disk Utility, if you put a floppy into the drive, can you use Disk Utility to mount the drive manually?

Try a different USB port?

There was no driver needed to support the USB drive for Mac OS 9 or later. If the drive no longer works, replace it. I suppose you could try a head cleaning kit first. I assume you tried some other micro-floppy. You DO know the drive only can read HD disks, the ones with two square holes, one of which is the write protect shutter. The old single sided 400K or double-sided 800 floppies it could never read. Those were written with a special variable speed controller created by the great Woz.

USB Floppy Drives used to work under 10.3 up to 10.6 Snow Leopard, but 10.7 didn't include a 64bit version of the floppy drive driver that was present in 10.6. So the drive will appear in Disk Utility but it will not be able to mount he floppy in it because it doesn't have a driver that tells it how to do it.

I have searched the Internet thoroughly but I could not find a driver that would work with recent versions of OS X. I have tried to copy the driver from 10.6 to 10.9 and obviously it didn't work (I knew it beforehand, but just for the sake of completeness. The obvious part is that from 10.7 and up, all Kernel Extensions have to be 64bit and the driver from 10.6 is 32bit).

If anyone can find the source code of one of those 10.6 drivers in a Darwin distribution and has the knowledge to do it, it could be patched and recompiled to work in 64bit mode… but I don't hold my breath and neither should anyone else.

The only two solutions I could come up with are:

a) finding an old machine with a floppy drive included in it and read the floppies to copy them over FTP to a modern OS X machine (maybe a USB stick would have worked, or burning a CD, but for me it was easier to just connect all machines to my network switch and find the minimum common denominator in file transfer technology = FTP). I did this the first time, but I had to fiddling with old machines and finding old software wasn't that easy (in my case it was not only a matter of reading the floppy contents but translate them to modern formats like Word .doc files or PNG images).

b) create a 10.6.8 VMWare virtual machine and attach the physical USB floppy drive to that booted virtual machine to read the disks I needed. With shared folders activated in the virtual machine, it was piece of cake to transfer everything. After updating and configuring the virtual machine to my likings with all the utilities and software needed I just need to keep the virtual machine file around and even if I upgrade to a newer OS X version, like 10.11.1 lately, I just need VMWare to keep everything working… God bless virtualization.

I keep a couple of special virtual machines in my servers in case I may need them in the future and several "well oiled" floppy drives to read more floppies in the future. This way I don' have to keep old machines around (that may brake over time) and I can just convert any floppy whenever I need with no fuss.

My two cents; your mileage my vary