BOOT.INI and ARC Path Naming Conventions and Usage

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SUMMARY

This article explains the conventions in the Advanced RISC Computing (ARC) specifications that are used to define the path to a Windows NT installation on Intel x86-processor-based computers and RISC-based computers. This article consists of the following sections:

  • x86-Based and RISC-Based ARC Paths Comparison
  • Differences Between the MULTI(X) and SCSI(X) Syntax and Application
  • Examples of x86-Based and RISC-Based ARC Paths

x86-Based and RISC-Based ARC Paths Comparison

The path to each Windows NT installation is described in a single line in the BOOT.INI file for x86-based computers, however, on RISC-based computers a set of four lines is used in the computer firmware BOOT- options to point to a single Windows NT installation. If there are multiple installations of Windows NT on your x86-based computer, the BOOT.INI has one ARC path for each installation in it. You are prompted with a boot menu during the boot process to choose the installation you want to boot.

There are two basic forms in which an ARC path can appear, one form starting with MULTI() and the other form starting with SCSI(). Both forms are used on x86-based computers, however, only the SCSI() form is used on RISC computers:

x86-Based Computers

The following are generic examples of two possible BOOT.INI ARC paths:
multi(X)disk(Y)rdisk(Z)partition(W)\<winnt_dir>

-or-

scsi(X)disk(Y)rdisk(Z)partition(W)\<winnt_dir>


where X, Y, Z, and W are numbers that identify the item to their left.

Both ARC-path examples above allow Windows NT find the %SystemRoot% directory to complete the boot process by loading files in that reside in that directory. For additional information, see the Differences Between The MULTI(X) And SCSI(X) Syntax And Application section below.

RISC-Based Computers

Because the RISC-based architecture requires that the firmware points to different areas of the system, the ARC path to a single Windows NT installation consists of a group of four definitions with ARC paths (versus only a one-line ARC-path definition on x86-based computers). Each ARC path that follows one of the four definitions starts with SCSI() after the definition name:

   SYSTEMPARTITION scsi(X)disk(Y)rdisk(Z)partition(W)
   OSLOADER  scsi(X)disk(Y)rdisk(Z)partition(W)\os\<nt_dir>\osloader.exe
   OSLOADPARTITION scsi(X)disk(Y)rdisk(Z)partition(W)
   OSLOADFILENAME  \<winnt_dir>
				


The following explains each line of the four-line group above.

Definition 1 (SYSTEMPARTITION):
Defines the path to the SYSTEMPARTITION, the small, File Allocation Table (FAT) partition which holds OSLOADER.EXE and HAL.EXE:

scsi(X)disk(Y)rdisk(Z)partition(W)


Definition 2 (OSLOADER):
Defines the path to the OSLOADER file. This is the same as the SYSTEMPARTITION, but it includes a path descriptor:

scsi(X)disk(Y)rdisk(Z)partition(W)\os\<nt_dir>\osloader.exe

where <nt_dir> indicates the directory in which OSLOADER.EXE resides.


Definition 3 (OSLOADPARTITION):
Defines the boot partition which contains the rest of the Windows NT system files:

scsi(X)disk(Y)rdisk(Z)partition(W)


Definition 4 (OSLOADFILENAME):

Defines the name of the Windows NT installation directory (winnt_dir) with no drive letter:

\<winnt_dir>


Differences Between the MULTI(X) and SCSI(X) Syntax and Application

MULTI(X) Syntax

The MULTI(X) syntax of the ARC path is only used on x86-based computers. In Windows NT version 3.1 this path is only valid for IDE and ESDI drives; in Windows NT version 3.5, 3.51 and 4.0 it is valid for SCSI drives as well.

The MULTI() syntax indicates to Windows NT that it should rely on the computers BIOS to load system files. This means that the operating system will be using interrupt (INT) 13 BIOS calls to find and load NTOSKRNL.EXE and any other files needed to boot Windows NT.

The X, Y, Z, and W parameters have the following meaning:

  • X is the ordinal number of the adapter and should always be 0 (see the text below for the reason).
  • Y is always 0 (zero) if the ARC path starts with MULTI(), because MULTI() invokes the INT 13 call as described above and therefore does not need the DISK() parameter information.
  • Z is the ordinal for the disk on the adapter and is usually a number between 0 and 3.
  • W is the partition number. All partitions receive a number except for type 5 (MS-DOS Extended) and type 0 (unused) partitions, with primary partitions being numbered first and then logical drives. NOTE: The first valid number for W is 1, as opposed to X, Y, and Z which start at 0 (zero).
Theoretically, this syntax could be used to start Windows NT on any drive in the system. However, this would require that all drives are correctly identified through the standard INT 13 interface; since support for this varies from disk controller to disk controller and most system BIOS only identify a single disk controller through INT 13, in practice it is only safe to use this syntax to start Windows NT from the first two drives connected to the primary disk controller, or the first four drives in the case of a dual-channel EIDE controller.

In a pure IDE system, the MULTI() syntax will work for up to the four drives maximum on the primary and secondary channels of a dual-channel controller.

In a pure SCSI system, the MULTI() syntax will work for the first two drives on the first SCSI controller (that is, the controller whose BIOS loads first).

In a mixed SCSI and IDE system, the MULTI() syntax will work only for the IDE drives on the first controller.

SCSI(X) Syntax

The SCSI() syntax is used on both RISC and x86-based computers and is used in all versions of Windows NT. Using SCSI() notation indicates that Windows NT will load a boot device driver and use that driver to access the boot partition.

On an x86-based computer, the device driver used is NTBOOTDD.SYS, which can be found in the root of the system drive (generally of drive C) and is a copy of the device driver for the drive controller in use.

On a RISC computer, the driver is built into the firmware as required by the RISC standards, so no file is required.

The X, Y, Z, and W parameters have the following meaning when using the SCSI() syntax:

  • X is the ordinal number of the adapter as identified by the NTBOOTDD.SYS driver.
  • Y is the SCSI ID of the target disk.
  • Z is the SCSI logical unit number (LUN) of the target disk. This number is almost always 0 (zero).
  • W is the partition number. All partitions receive a number except for type 5 (MS-DOS Extended) and type 0 (unused) partitions, with primary partitions being numbered first and then logical drives.

    NOTE: This first valid number for W is 1, as opposed to X, Y, and Z which start with 0.
When using SCSI() notation the value of X depends upon NTBOOTDD.SYS. Each SCSI driver under Windows NT has its own method of ordering controllers, although generally they conform to the order that the BIOS on the controllers load (that is, if the BIOS is loaded).

Additionally, if you have multiple controllers that use different device drivers, you should only count those controlled by NTBOOTDD.SYS when determining the value of the X parameter. For instance, if you have an Adaptec 2940 (which uses the driver AIC78XX.SYS) and an Adaptec 1542 (which uses AHA154X.SYS) X will always be 0. What will change is the NTBOOTDD.SYS file:

  • If you load Windows NT from a drive on the Adaptec 2940, NTBOOTDD.SYS is a copy of AIC78XX.SYS.
  • If you load Windows NT from a drive on the Adaptec 1542, NTBOOTDD.SYS is a copy of AHA154X.SYS.

Example of x86-Based and RISC-Based ARC Paths

The following are examples of valid ARC paths. The first two examples are ARC paths on x86-based computers. Example three is taken from a single boot entry on a DEC Alpha AXP 150 RISC-based computer, but should be correct for all RISC-based computers with similar drive configurations.

NOTE: If you have multiple ARC paths in the BOOT.INI file and a combination of different SCSI adapters in your computer as shown in example 1 and 2 below, you must copy the appropriate SCSI driver to the NTBOOTDD.SYS file name in the root directory of the system partition (generally drive C), before you shut down to boot from a Windows NT installation that resides on a drive connected to the other SCSI controller. This is because regardless on which drive the other Windows NT installation resides, NTBOOTDD.SYS always resides on the system partition.

Example 1: Multiple SCSI controllers

This is an example of an x86-based computer with the following drives and controllers installed:

  • Two Adaptec 2940 SCSI controllers, each with two 1 gigabyte (GB) hard drives at ID 0 and 1.
  • One Adaptec 1542 SCSI disk controller, with two 1 GB hard drives at ID 0 and 4.
Each hard drive has a single, 1 GB primary partition. For the purpose of explaining this example, the partitions are numbered from 1 through 6, with partition 1 and 2 identifying disk one and two attached to the Adaptec 2940 controller, partition 3 and 4 identifying the disks attached to the second Adaptec 2940 controller, and partition 5 and 6 on the disks on the Adaptec 1542. One of the following ARC paths appears in BOOT.INI depending on what partition you installed Windows NT. This example assumes that Windows NT is installed in a directory named WINNT35:

Windows NT Installed On Corresponding ARC Path

Partition1(on 1st Adaptec 2940) multi(0)disk(0)rdisk(0)partition(1)\WINNT35
Partition2(on 1st Adaptec 2940) multi(0)disk(0)rdisk(1)partition(1)\WINNT35
Partition3(on 2nd Adaptec 2940) scsi(1)disk(0)rdisk(0)partition(1)\WINNT35
Partition4(on 2nd Adaptec 2940) scsi(1)disk(1)rdisk(0)partition(1)\WINNT35
Partition5(on Adaptec 1542)     scsi(0)disk(0)rdisk(0)partition(1)\WINNT35
Partition6(on Adaptec 1542)     scsi(0)disk(4)rdisk(0)partition(1)\WINNT35
				


NOTES: For partition 3 and 4, NTBOOTDD.SYS is a copy of AIC78XX.SYS, for partition 5 and 6 NTBOOTDD.SYS is a copy of AHA154X.SYS. As an alternative to the ARC paths of partition 1 and 2, you can substitute the following paths provided that you have an NTBOOTDD.SYS file that is a copy of the AIC78XX.SYS driver:

Windows NT Installed On Corresponding ARC Path

Partition1(on 1st Adaptec 2940) scsi(0)disk(0)rdisk(0)partition(1)\WINNT35
Partition2(on 1st Adaptec 2940) scsi(0)disk(1)rdisk(0)partition(1)\WINNT35
				


However, Windows NT Setup always uses MULTI() syntax for these first two drives.

Example 2: Mixed IDE and SCSI Environment

This is an example of an x86-based computer with the following drives and controllers installed:

  • A dual-channel EIDE controller with three 1 GB drives, two on the primary channel and one on the secondary channel.
  • An Adaptec 2940 SCSI controller with a single 4 GB hard drive at ID 3.
The three EIDE drives have one 1 GB partition each, the SCSI drive has four 1 GB partitions. For the purpose of explaining this example, the partitions are numbered from 1 through 7, with partition 1 and 2 identifying disks one and two on the primary channel of the EIDE controller, partition 3 on the secondary channel, and partitions 4, 5, 6, and 7 on the SCSI drive. One of the following ARC paths appears in BOOT.INI depending on what partition you installed Windows NT. This example assumes that Windows NT is installed in a directory named WINNT35:

Windows NT Installed On Corresponding ARC Path

Partition1 (pri. EIDE channel) Multi(0)disk(0)rdisk(0)partition(1)\WINNT35
Partition2 (pri. EIDE channel) multi(0)disk(0)rdisk(1)partition(1)\WINNT35
Partition3 (sec. EIDE channel) multi(0)disk(0)rdisk(2)partition(1)\WINNT35
Partition4 (on Adaptec 2940)   scsi(0)disk(3)rdisk(0)partition(1)\WINNT35
Partition5 (on Adaptec 2940)   scsi(0)disk(3)rdisk(0)partition(2)\WINNT35
Partition6 (on Adaptec 2940)   scsi(0)disk(3)rdisk(0)partition(3)\WINNT35
Partition7 (on Adaptec 2940)   scsi(0)disk(3)rdisk(0)partition(4)\WINNT35
				


NOTES: Loading Windows NT from partitions 4 through 7 requires an NTBOOTDD.SYS file which is a copy of AIC78XX.SYS.

Example 3: Boot variables on a DEC Alpha AXP 150

On a RISC computer, all boot paths are defined through the firmware. When creating a new boot entry for a RISC computer the firmware steps you through a series of prompts which aids you in defining the paths correctly; so unless you are editing a boot entry that is not working any more, you should never have to directly edit the ARC paths on a RISC computer.

The following example is a boot entry on a DEC Alpha AXP 150, with a single hard drive at ID 0 that is partitioned as follows:

  • One 4 MB system partition.
  • One 396 MB boot partition.
Windows NT is installed on the boot partition in a directory named WINNT35 and the OSLOADER directory is also named OS\WINNT35, however, it is on the system partition. The boot entry has the following values:

   SYSTEMPARTITION scsi(0)disk(0)rdisk(0)partition(1)
   OSLOADER  scsi(0)disk(0)rdisk(0)partition(1)\os\winnt35\osloader.exe
   OSLOADPARTITION scsi(0)disk(0)rdisk(0)partition(2)
   OSLOADFILENAME  \WINNT35
				

Properties

Article ID: 102873 - Last Review: November 1, 2006 - Revision: 3.1
APPLIES TO
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Advanced Server 3.1
Keywords: 
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