Disk drives on the PC2086

[PortoManc]

I remember back in 1986, as a student, I had my first own PC - the Amstrad PC2086, bought from Time Computers (then of Blackburn, Lancashire). As Amstrad had been having problems with their own internal HDDs at the time, the spec of the machine I got was a 1 internal floppy drive (3 1/2", 720kb) with a 30 Mb Hard card, partitioned into a 20 Mb OS & software drive C: and a 10 Mb data partition D:. That was in an expansion slot at the back. In addition, I had a 5 1/4", 360kb external drive. 
Now, as a now-retired data programmer, I can set up virtual emulators of that early machine, especially if I use 86Box, which allows me to build a specific Amstrad PC2086 'box'. I can add a virtual hard drive, and virtual floppy drives (both 3 1/2" and 5 1/4"). In theory 86Box can allow me to add up to 4 floppy drives of various specs (360kb, 720kb and 1.44Mb), although I haven't tried it. I've still got my original Amstrad PC2086 manuals as well, and the User Guide goes into detail about the Floppy Disk controller (sections 8.2 and 8.3). It also suggests that it's necessary to set a DIP switch to get the machine to read the external drive, which then becomes the drive B:.
Now, my query is whether anyone has tried a configuration of a machine that has TWO internal 3 1/2" drives, with a HDD card in the expansion slots and also (maybe via an expansion slot) an external 5 1/4" drive? Is that even possible, and if so, given that A: and B: normally designate the floppy drives in MS-DOS and C: the first HDD, what would the 3rd drive's letter be? I'd also be interested to know if anyone has tried or replicated that drive configuration in a Virtual Machine such as 86Box, and how did they fare?  Just out of curiosity, of course.
    

[JohnElliott]

In general: On MSDOS 3.3 and prior, floppy drives get letters allocated before hard drives. So a three-floppy machine would have floppies A: B: and C: with the hard drive as D:. On later versions the first two floppies would get letters, then hard drives, then any other floppies. See https://en.wikipedia.org/wiki/Drive_letter_assignment

Specifically on the 2086, the built-in BIOS doesn't support more than two floppy drives. Any further floppy drives would need an expansion card with its own BIOS, or a driver loaded in CONFIG.SYS. 

[PortoManc]

Thanks, JohnEliott, for your reply. I had thought an expansion card in the 'back end' of the machine would have been the way to go with the Amstrad, but unfortunately I neither have access to my actual Amstrad (which is back home at my mum's 'in the loft'), and it's also a 'Dead on arrival' anyway so I couldn't try out a physical attempt at multiple drives, even if I had additional physical floppy drives available. The version of MS-DOS installed on my virtual Amstrad (running in 86Box) is indeed MS-DOS 3.30. I was able to download images of the Amstrad setup disks a while back (I think either from WinWorldPC.com or archive.org (both of which are a source of 'abandonware' and earlier versions of software). Using my original manuals I had still kept from my 2086, I was able to set up a 50Mb hard drive, partitioned into two drive partitions, C: and D:, as well as creating the 'virtual' A: and B: drive (3.5" 1.44M and 5.25" 360kb respectively), but was curious as to whether I could create a third (or more) floppy drive(s), since 86Box allows me to add ATAPI and SCSI peripheral devices, although only shows two 'floppy drive' icons in the status bar of the bottom of the 86Box window.
I was also curious as to what drive letters those extra floppy drives were given. I remember years and years ago, my dad had a two volume technical manual and user guide to MS-DOS 3.30, which gave information about (as far as I remember), various interupts and machine code program-ettes. Unfortunately I have not been able to track those books down and think he must have returned them at sometime when he returned his work IBM PC clone computer to his office, during the mid-'90s!