I have a simple Linux disk image that is made with syslinux and I want to boot it from a USB key. I originally partitioned the image with parted, so it has a partition table and the first partition is marked as bootable.
I dd'd the image to a USB key, and it will boot on a PC I have (call it computer A) but it won't boot another PC (computer B) that I need to use. So I know the image is legit.
If I take the same USB key, use unetbootin and make a bootable key with a Fedora ISO, it will boot on Computer B... So Computer B definitely supports booting from USB keys.
Here's the difference though: With the Fedora image, the USB key shows up as a hard disk (USB-HDD0) in the boot menu but with my custom disk image it shows up as a removable drive (USB-ZIP0).
What controls whether a USB key shows up as a hard disk or as a removable drive?
As per K7AAY's request I made a gparted live usb, ran
echo "0 0 0" > /sys/class/scsi_host/host0/scan
and there is no output. I tried host0 thru host4, no output. I don't know what that command is supposed to do.