Timothy Daniels said:
I was hoping that you'd be able to explain it. But....
I don't know the details (and unlike some, I'll admit that...) but
here is what I do know.
For Windows PE to boot from USB, it is done from a RAM disk load as
Stephan indicated in an earlier post.
As far as Windows XP Embedded goes, USB bootable solutions are a
relatively recent feature. As I understand it, they've tweaked things
to allow the USB drivers to load earlier in the boot process. Since
none of the XP Embedded solutions I've dealt with used it, I never
looked to closely at it. There was a lot of chatter in
microsoft.public.windowsxp.embedded a few years back about why one
particular manufacturer was able to supply USB bootable solutions that
others couldn't, and then MS came out with Feature Pack 2007 that
included USB boot as an option. You might ask in
microsoft.public.windowsxp.embedded for more info.
Likely the biggest reason MS hasn't done this in the mainstream
Windows versions has to do with licensing. That, and usability - if
booting to an external USB device means that you will be booting
multiple, different machines with the device, you need different
drivers, and in some cases even different HALs. What a nightmare that
would be. XP Embedded avoids this by being custom built for a
particular device, including the correct HAL and drivers. Each new
hardware platform needs a new XP Embedded build.