BOOT.INI is the Windows Boot Configuration file, called by NTLDR (NT Loader). It is surpassed by the Windows Boot Configuration Data Store in Windows Vista and later. The boot.ini file can be edited using MSConfig (System Configuration), which contains options such as timout, safe mode and No GUI Boot.
An example of a boot.ini file:
[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
If there is only one operating system present in boot.ini, the NTLDR boot menu does not appear, and insted defaults to the first OS listed. The lowest timeout possible to set is 3 seconds.
Causes Windows to write a log of the boot to the file %SystemRoot%\Ntbtlog.txt.
Enables kernel-mode debugging.
Enables kernel-mode debugging and specifies an override for the default serial port.
Switches system into 640x480 16-color VGA mode. It uses a generic video driver compatible with every video adapter.
Limit the amount of RAM that windows can use.
Disables the bitmap that displays the loading screen on Windows startup.
Sets the number of processors that Windows wil run at startup. Speculation as if it works to speed up boot times.
Uses a different kernel, for example "/KERNEL=WRKx86.exe" would use <WindowsDir>\System32\wrkx86.exe as the Kernel
Uses a different HAL dll, for example "/HAL=halmacpi.dll" would use <WindowsDir>\System32\halmacpi.dll as the HAL
Shows all the loaded files, then runs CHKDSK.
Boots the computer on a certain year, for example "/YEAR=2000" would start Windows at year 2000.