The checked build of Windows has lots of additional cross-checks, what we at OSR call "reasonableness checks," that are performed on operating system data structures and function call arguments passed from drivers. No driver has been sufficiently tested for release until it runs on the checked build without displaying obvious problems. Let me repeat myself for emphasis: No driver has been sufficiently tested until it has run on the checked build without problems. This means: You?ve got to test on the checked build. Period.

First, You Have To Find It
Obviously, you can?t install the checked build of the OS if you can?t find it. You can usually find the checked build for the latest version of the OS in your MSDN distribution. Alternatively, you can go to www.osronline.com and look for the little block labeled "The Latest" on the home page. In this block, you?ll see a link that reads "Checked Build Downloads" ? this link is kept up to date with the latest pointers to downloads of the checked build.

Of course, these files are likely to be executable install files.  No matter, just open the file (either the one you download or the one from MSDN) with WinZip or a similar utility and you can extract the specific checked files that you want.

Step 1: Identifying the Files to Install
There are several different versions of the operating system and HAL images supplied as part of the Windows distribution kit. These different versions exist to properly support specific combinations of processor and system hardware. When Windows is installed, the installation procedure automatically identifies which operating system image and HAL image to use, and copies the appropriate files to the %SystemRoot%\system32 directory of the system being installed.

The original names of the operating system image files as stored on the distribution media may include one or more of the following:

• NTOSKRNL.EXE - Uniprocessor x86 architecture systems with 4GB of physical memory or less.
• NTKRNLPA.EXE - Uniprocessor x86 architecture systems with PAE support, that is, more than 4GB of physical memory installed.
• NTKRNLMP.EXE - Multiprocessor x86 architecture systems with 4GB of physical memory or less.
• NTKRPAMP.EXE - Multiprocessor x86 architecture systems with PAE support, that is, more than 4GB of physical memory.

When copied to the %SystemRoot%\system32\ directory by the Windows installation procedure, the operating system image files and HAL use fixed, well known, names. This makes it easy for the loader to locate these files at boot time. The well-known names for these files are:

• NTOSKRNL.EXE - Operating system image for x86 systems with 4GB or less of physical memory;
• NTKRNLPA.EXE - Operating system image for x86 systems with PAE support, that is, more than 4GB of physical memory.
• HAL.DLL - Loadable HAL image.

During system installation, the installation procedure creates each of these files by copying the file appropriate for the system?s hardware from the distribution kit, and renaming it from its original name to one of the fixed names above.

The first step in installing the checked operating system image and HAL is to determine the original names of the images that were copied to your system during system installation. You do this by examining the file %SystemRoot%\repair\setup.log. An example of this file is shown in Figure 1. This file is used during the system installation process to copy files from the distribution medium to the %SystemRoot%\system32 directory.

[Paths]

TargetDirectory = "\WINNT"

TargetDevice = "\Device\Harddisk0\Partition1"

SystemPartitionDirectory = "\"

SystemPartition = "\Device\Harddisk0\Partition1"

[Signature]

Version = "WinNt5.1"

[Files.SystemPartition]

NTDETECT.COM = "NTDETECT.COM","f41f"

ntldr = "ntldr","3e8b5"

arcsetup.exe = "arcsetup.exe","379db"

arcldr.exe = "arcldr.exe","2eca9"

[Files.WinNt]

\WINNT\system32\drivers\kbdclass.sys = "kbdclass.sys","e259"

\WINNT\system32\drivers\mouclass.sys = "mouclass.sys","7e78"

\WINNT\system32\drivers\uhcd.sys = "uhcd.sys","10217"

\WINNT\system32\drivers\usbd.sys = "usbd.sys","5465"

(?several similar lines omitted?)

\WINNT\system32\framebuf.dll = "framebuf.dll","10c84"

\WINNT\system32\hal.dll = "halmacpi.dll","2bedf"

\WINNT\system32\ntkrnlpa.exe = "ntkrpamp.exe","1d66a6"

\WINNT\system32\ntoskrnl.exe = "ntkrnlmp.exe","1ce5c5"

\WINNT\inf\mdmrpci.inf = "mdmrpci.inf","96a3"

Figure 1 -- Example of %SystemRoot%\repair\setup.log

Again, regardless of which of the above files is installed, the non-PAE operating system image file is always called NTOSKRNL.EXE and the PAE operating system image file is always called NTKRNLPA.EXE when they are copied to the %SystemRoot%\system32\ directory. You can identify which operating system image files were installed on your system by searching setup.log for the above file names. Make a note of which operating system image files are used on your system, because you will need to copy the checked versions of these same files from the checked distribution kit. You will find the standard, well known, name of the operating system image file on the left of the equals sign, and it?s original name from the distribution medium immediately to the right of the equals sign on the same line.

In the example setup.log file shown in Figure 1 you can see that two operating system image files were copied to the \winnt\system32\ directory (which is %SystemRoot%\system32\) during installation. The file ntkrpamp.exe is copied from the distribution medium to ntkrnlpa.exe and the file ntkrnlmp.exe is copied from the distribution medium to ntoskrnl.exe.

Step 2: Getting and Copying the Checked Files
Now that you know which files to copy, you will need to copy the checked versions of these files to unique file names in the %SystemRoot%\system32\ directory. Find the files you have identified in the checked distribution kit.

Apparently, not everybody thinks finding the appropriate files is straight forward. Note that the checked distribution kit is most likely provided as a compressed executable archive named setup.exe or something similarly helpful. Thus, you?ll need to use a utility (I use Windows Commander, a knock-off of the venerable Norton Commander, but I?m sure there are others) to extract the files from the executable archive. In Windows Commander, you just select the executable and type ctrl/page-down to open the executable archive. Alternatively you can just run the executable on the wrong version of the system, causing it to fail, perhaps aborting it in the process. This will leave the files from the checked build in a temporary install directory where you can grab them. You can thank SNoone for that last suggestion. I?m sure none of you are surprised that he would come up with such an idea.

Once you?ve found the files you want, copy them to the %SystemRoot%\system32\ directory of your system, giving them new, unique, file names. The copies of these files may be named just about anything you like, however the file names must adhere to the 8.3 naming convention.

One way to ensure unique, 8.3-compliant, file names is to rename the file types from their original file types (.dll or .exe) to .chk when they are copied. Thus, using the example started previously, we would copy files from the checked distribution kit as seen in Figure 2.

Original File Name on Checked Distribution	File Name Copied to in %systemroot%\system32\
Ntkrnlmp.exe	ntkrnlmp.chk
ntkrpamp.exe	ntkrpamp.chk
halmapic.dll	halmapic.chk

Figure 2 -- Renaming Checked Distribution

Some files in the checked distribution are provided in compressed form. These files are indicated with an underscore character as the last character in their file type. For example, if you look for the file halapic.dll in the checked build distribution, but you find the file halapic.dl_ you have found the correct file but it is compressed.

To decompress compressed files from the checked distribution, use the expand utility found in the %SystemRoot%\system32\ directory. For example, to expand halapic.dl_ and name the expanded file halapic.chk you can use the following command from a command prompt window:

Step 3: Editing 'boot.ini"
Once you have copied the checked files to the %SystemRoot%\system32\ directory, you will need to create a boot-time option that allows the system to be started using these checked files. You do this by editing the file boot.ini.

Boot.ini resides in the root directory of the boot volume of your system, and is normally set as a "hidden" and "system" file. As a result, it typically will not be displayed by the default "dir" command from a command prompt window. You may verify the existence and attributes of boot.ini using the "attrib" command from a command prompt window. Once you have verified that you can find boot.ini, you must change its attributes so that it is no longer marked as being either "hidden" or "system". This can be done using the following command:

See the example in Figure 3.

Figure 3 -- Locating and Setting Attributes in "boot.ini"

Once the "system" and "hidden" attributes have been removed from boot.ini, you can edit the file with a text editor such as Notepad. The goal of editing boot.ini is to create a new boot-time option that allows you to start the system with the checked version of the operating system image and HAL that you previously copied to %SystemRoot%\system32\.

When you begin your editing session, the unmodified version of boot.ini will look something like the example shown in Figure 4.

Figure 4 -- Example of file "boot.ini" Before Editing

The file boot.ini controls the operating system options that are displayed at boot time. The example file in Figure 4 shows a computer with a single operating system installed. It is possible that the version of boot.ini on your system has multiple lines under the [operating systems] heading. This will be the case if you have more than one operating system (or operating system version) installed on the computer, such as if you have both Windows Server 20003 and Windows XP installed on the same computer, or you have a Beta and released version of Windows XP installed on the same computer.

Locate the line that describes the operating system for which you want to install the checked operating system image and HAL. You can identify this system by the name of the %SystemRoot% directory which appears after the first backslash in each of the lines in the [operating systems] section. In Figure 4, the %SystemRoot% directory for the one system image in boot.ini is named \WINDOWS.

Once you have located the line that describes your desired operating system, make a copy of the line, and paste it at the end of boot.ini, in the [operating systems] section, on a line by itself. The result is shown in Figure 5.

Figure 5 -- Coping the Desired Operating System Line

Continue editing boot.ini, and add to the end of the copied line the following options: