format a:

does an endless loop.

Edit: oh, going back I got an JS popup:

  Unable to restore disk 'PC-DOS 2.00 (Disk 1): 
  sector (CHS=0:1:0) out of range (9 changes applied)

After pressing the reset button:

  Non-System disk or disk error
  Replace and strike any key when ready

I had to press load disk A button, to start fresh. Quite impressive.

And then I just found out to load Windows 1 with mouse support. Wow. Made my day. Epic!