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Windows Requirements for Boot Devices
The best thing about adding another bootable bus to Windows is that manufacturers can take advantage of much of the existing Windows boot process. As long as a new device looks and behaves like existing devices while NT Loader loads the system, new devices can be made to work like old devices. The goal for booting Windows from a USB device is to use as much of the existing Windows boot process with as little change as possible.

This paper focuses solely on booting from hard disk drives and CD-ROM drives for recovery and deployment purposes. Windows as it exists today is currently not optimized to run as an installed operating system from USB attached mass-storage or CD.

The USB Mass Storage support consists of storage protocols over USB that enable USB hard disk drives and USB CD-ROM drives. All storage devices that are to be boot devices for Windows should behave like one of those two categories to take advantage of the existing boot process. DVD-ROM drives fit into the category of CD-ROM drives for the purpose of this document.

BIOS must support INT 13h During the boot process, Windows assumes that support for communicating with the boot device, either hard disk drive or CD-ROM drive, is present in INT 13h when Windows loads because the NT Loader uses calls to INT 13h to access the disk. INT 13h support must comply with the "BIOS Enhanced Disk Drive Services - 2" specification and the "USB Mass Storage Specification for Bootability," The newer specification is considered the authority if the two specifications contradict each other.

Accurate drive numbering by BIOS Windows also requires that the assignment of drive numbers follows "Compaq Phoenix Intel BIOS Boot Specification version 1.01." Hard disk drives should begin numbering at 80h and CD-ROM drives should begin numbering at 82h, as in the past.

In this paper, the remainder of the requirements, along with recommendations for component manufacturers, has been organized by the different components that play a part in booting.