From: John Beckett 

"Geo"  wrote in message
news::
> I took your point, it's only slightly different from a removeable hd though.
> All removeable storage devices that have boot capabilities have this
> ability, the only difference here is that the USB device is using a named
> file instead of having to use a boot sector.

The autorun.inf file that I described is not related to booting from a USB
drive. I don't know what a mobo BIOS does when it boots from a USB, but
presumably it is exactly the same process as when it boots from a floppy -
the BIOS would load the first sector and execute code from it if certain
sanity checks are met. Or, maybe it's like a hard drive where first the
BIOS reads the MBR to find the active partition.

The autorun.inf file is handled by our old friend Explorer, not the BIOS.

> Have you ever noticed how an NT4 CD doesn't ask if you want to boot from CD
> but a W2K CD does? That code is in the boot code on the CD.

Yes. There is a "boot image" file on a bootable CD. For a Windows
CD, the file is called "Microsoft Corporation.img" but it's not
in the normal file system - it's 2KB and in a special location for booting.

The img file is loaded and executed by the BIOS if set to boot from CD. The
img file loads and runs files from CD: BOOTFIX.BIN
SETUPLDR.BIN

The BOOTFIX.BIN file contains the text: Press any key to boot from CD.

John

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