A is the disk signature (e.g., 6c156c97); the other variables are the same as for the SCSI syntax. A is a unique hexadecimal number that Win2K Setup writes to the Master Boot Record (MBR) during the Setup process's text-mode portion.
Using the signature syntax forces NT Loader (NTLDR)—the first file that Win2K launches to start the OS—to locate whichever drive has a disk signature that matches the A value during OS startup. Keep in mind that this drive might connect to a different SCSI controller number than when you first installed Win2K if you've added SCSI controllers to the machine. As with the SCSI syntax, the signature syntax requires a copy of the specific SCSI driver, renamed ntbootdd.sys, on the drive's root.
Win2K Setup determines that it should use the signature syntax under certain conditions. The most common conditions are when the drive has more than 1024 cylinders (which creates a problem if any cylinder number greater than 1024 is in the system partition) or when the SCSI controller's BIOS is disabled.
Tweaking Boot.ini
You can edit boot.ini to change or enhance the startup process. You can also edit the file to troubleshoot a computer that's having problems.
Changing the default OS. You can change a system's default OS and the length of the timeout that boot.ini offers users. You can make these modifications without editing the boot.ini file; simply use the System Properties dialog box. (To quickly access this dialog box, right-click My Computer and choose Properties from the shortcut menu.) Move to the Advanced tab, and click Startup and Recovery to open the Startup and Recovery dialog box, which Figure 2 shows. Select the desired OS from the Default operating system drop-down list in the System startup section.
Use the section's Display list of operating systems for x seconds option to change the timeout specification. Don't shorten the time to less than 10 seconds or users won't have time to read the options and select one. (Although you can clear the box to prevent display of the onscreen menu, I recommend against it. If you have to perform some administrative task that involves another OS, you'll need to go through all these steps again to redisplay the menu and gain access.)
In Win2K, you can't specify 1 as the timeout duration to leave the menu on the screen until the user makes a choice, as you can in Windows NT. Win2K's Startup and Recovery dialog box doesn't accept a negative number. If you manually edit boot.ini and change the timeout duration to 1, Win2K ignores the entry and resets the timeout to the previous specification during the next boot.
To keep the menu onscreen, a user can press any key except the Enter key (e.g., users can click an arrow key to highlight a different choice). Of course, this trick requires user intervention, so it is of no help unless the user is available to press a key. The user can't turn on the computer and head for the coffee machine and expect the menu to still be onscreen when he or she returns.
Troubleshooting. Boot.ini takes a substantial number of parameters, most of which are useful under specific conditions—usually when you're troubleshooting a serious problem. The file also requires certain switches to support specific hardware configurations. Table 1 lists several common boot.ini switches and their functions.
Creating an emergency boot disk. If one of the Win2K startup files is missing or corrupt and the Windows File Protection (WFP) feature fails to correct the problem automatically, you can usually boot with a Win2K boot disk to replace the file. Because OS startup is totally dependent on the information in boot.ini, you must provide a boot.ini file on the boot disk, even if boot.ini isn't the corrupted or missing file.
To create a boot disk, format a 3.5" disk on another Win2K computer. Copy NTLDR and ntdetect.com from that computer's root to the 3.5" disk. These files aren't version specific, so the source computer can be running any version of Win2K Server or Win2K Professional.
If the source computer has exactly the same hard disk setup (i.e., same drive type, same drive, and same partition for the OS installation) as the computer you're troubleshooting, you can copy and use the source computer's boot.ini file as is. Otherwise, copy the boot.ini file onto the 3.5" disk, gather the necessary information about the destination computer's physical drive type, and edit the file's [operating systems] section information to create a viable boot.ini. Use the boot disk to boot the destination computer, and overwrite the corrupted file or files from the 3.5" disk.
Understanding what boot.ini does, and how it does it, gives you the power to control the OS startup process. This capability is especially important if you need to troubleshoot a computer that's producing blue screens of death because Microsoft Product Support Services (PSS) might ask you to edit boot.ini and add switches that help the debugging effort.