Signature() syntax is used only if one of the following conditions exists:
The System BIOS or controller hosting the boot partition on which Windows is installed, does not support INT-13 EXTENSIONS, or has the INT-13 Extensions option disabled, and the partition on which you installed Windows is either larger than ~7.8 gigabytes (GB) in size, or the ending cylinder number for that partition is higher than 1024.
The drive on which you installed Windows is connected to a SCSI controller whose BIOS is disabled, so INT13 BIOS calls cannot be used during the boot process.
For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
242518 Long Pause During Windows 2000 Startup Process
The signature() syntax is equivalent to the scsi() syntax, but is used instead to support the Plug and Play architecture in Windows. Because Windows is a Plug and Play operating system, the SCSI controller number instance may vary each time you start Windows, especially if you add new SCSI controller hardware after Setup is finished.
Using the signature() syntax instructs Ntldr to locate the drive whose disk signature matches the value in the parentheses, no matter which SCSI controller number the drive is connected to.
The signature() value is extracted from the physical disk's Master Boot Record (MBR). This unique hexadecimal number is either written to the MBR during the Text-mode portion of Setup, or is written by an installation of Microsoft Windows NT version 4.0 or earlier.
NOTE: If the disk signature in the MBR gets overwritten (for example, by a virus) or changed (corrupted) so that it no longer matches the signature() value in the Boot.ini file, you may receive the following error messages when you start the computer:
Windows 2000 could not start because of a computer disk hardware configuration problem. Could not read from selected boot disk. Check boot path and disk hardware. Please check the Windows documentation about hardware disk configuration and your hardware disk configuration and your hardware reference manuals for additional information.
Windows could not start because of the following ARC firmware boot configuration problem: did not properly generate ARC name for HAL and system paths. Please check the Windows documentation about ARC configuration options and your hardware reference manuals for additional information.
Because the signature() syntax replaces the scsi() syntax, the same requirement applies in that a file named Ntbootdd.sys is required in the root folder of the system partition to address the SCSI controller at startup. This file is the specific SCSI miniport device driver for the SCSI adapter from which you are booting, renamed to Ntbootdd.sys and placed in the root folder of the system drive.
For additional information about ARC names in the Boot.ini file, please see the following article in the Microsoft Knowledge Base:
102873 Boot.ini and ARC Path Naming Conventions and Usage