Syslinux - Oct 2004 - memdisk and usb flash devices as primary hard drives.

Has anybody tried to boot a dos disk via memdisk with a usb flash device 
as a primary hard drive?

I have a 512MB flash key that when connected becomes my primary hard 
drive (new bios) - 0x80.  If I boot a MS-DOS 7.10 floppy, one gets the 
command prompt and I can see the contents of my flash key as drive C:.

But, if I make a image of the floppy and boot the image via memdisk, 
then memdisk loads the floppy image to ram and tries to boot it but 
fails - the system just hangs after saying "Loading boot sector... 
booting...".

If you try to boot PC-DOS 7.0 via memdisk, then after seeing "Loading 
boot sector... booting...", PC-DOS reports "Starting PC-DOS..."
and then
hangs (but boots fine if booting from a physical floppy).

If I disconnect my flash key and boot again via memdisk, then booting is 
successful and I get a command prompt where I see my IDE disk as drive C:.

I have tested the problem both under pxelinux and under grub.  Syslinux 
seems to have problems installing itself onto the flash key - 
ldlinux.sys gets loaded onto the partition, I can see it modified the 
boot sector of the partition, the partition is also marked bootable 
(0x80),  but the mbr code just reports "Missing operating system" when
I
try to boot from the usb key.

Grub, on the other hand has no problems booting from the usb key (tried 
both version 0.93 and the latest cvs version).

Quinn

Addendum to the above tests:

I just tried booting a gzipped compressed hard disk image with the usb 
key in - same problem - hangs just after memdisk
loads the image to ram and tries to boot.  If I take the key out, then 
the problem goes away.

Also, after re-reading the subject line - I can see that it might be 
misread incorrectly.
It should probably be read as "memdisk with usb flash devices as primary 
hard drives."

Quinn