I finally found some time to work on 5.0rc2. For the past week, I have been playing with USB driver under DOS.
There seems to be two nextgen branches of DOS USB drivers:
My experience wasn't too great, and reminded me of the time when I was trying to get NTFS working under DOS. None of the drivers I tried would let me reliably mount a 1GB USB memory stick under various machines (assorted Dell notebooks, NEC Versa notebook, an oldish Compaq desktop, a self-built Intel desktop etc.). Common problems include hang during scanning, invalid opcode etc.
At first, I thought it was due to FreeDOS. Upgrading to the latest kernel didn't help. So I replaced it with MS-DOS 7.0 but got the same problems.
In contrast, Parted Magic let me access the USB memory stick with 0 problems on all these machines. I think a common use case for UBCD is to rescue files from a bad system to a USB storage device, and for that I think DOS USB doesn't meet the requirement at the moment. Having to fiddle with all the driver parameters is bad enough when you already have one problem on your hand (to rescue files from a bad system). Not able to get it to work after all this effort is just too much!
I would like your opinions on this, but I think DOS is really _not_ suitable for more complex tasks like NTFS access or USB support. I am sure it can be done on some systems with some parameters, but it is just too much trouble to get it working (if at all)! As such, I think I'm not going to pursue further on DOS USB support, but leave it to Linux (i.e. Parted Magic) like the case of NTFS.