Boot.ini Switches

When the boot.ini line appears on my Windows NT Server 4.0 system's screen, I see the /basevideo switch. Why does this switch appear?

What are boot.ini switches and what are their uses? Two types of switches exist: switches that you use for debugging (i.e., debug switches) and switches that you use for running the computer under special circumstances (i.e., runtime switches).

Information about debug switches is easy to find. Following is a list of debug switches, complete with their uses:

  • /basevideo. Forces the system into standard 640 * 480 16-color VGA mode. You use this switch to install a new driver or change refresh rates.

  • /baudrate=nnn. Sets the debug port's baud rate (e.g., /baudrate=9600). The default baud rate is 19,200. The normal rate for remote debugging over a modem is 9600. This switch automatically enables the /debug switch.

  • /crashdebug. Enables COM port use for debugging in the event of a crash. In this situation, you can use the COM port for normal operations while NT is running, but the system will automatically convert the port to a debug port if NT crashes. This switch causes NT to load the kernel debugger during the boot, then swap out the pagefile after the boot. Therefore, a support technician can't break in to the debugger unless NT is suspended at a kernel STOP screen.

  • /debug. Enables the kernel debugger, thereby allowing live remote debugging of an NT system through the COM ports. Unlike /crashdebug, /debug uses the COM port regardless of whether the system crashes.

  • /debugport=comx. Selects a COM port for the debug port (e.g., COM 1, COM 2, COM 3). The /debugport switch defaults to COM 2 if that port exists; otherwise, it uses COM 1. This switch enables the /debug switch.

  • /maxmem=nn. Selects the amount of memory that NT detects and uses at startup. You should never set the nn variable to less than 12 (which represents NT 4.0's minimum amount of memory). This option is useful for checking for bad memory chips.

  • /nodebug. Disables the kernel debugger. This switch is useful for returning debug-mode machines to runtime mode.

  • /sos. Causes NT Loader (NTLDR) to show the names of modules while NT devices load. Dots will no longer appear on your screen as the system loads.

  • Information about runtime switches can be fairly difficult to obtain. Following is a list of runtime switches, complete with their uses:

  • /3gb. Lets user-mode applications access 3GB of memory instead of the usual 2GB that NT allocates to user-mode applications. This switch is available only on NT Server 4.0, Enterprise Edition, Service Pack 3 (SP3).

  • /noserialmice:comx. This switch disables mouse-device use on the specified COM port. To disable more than one port, you can separate parts with commas. If you use /noserialmice without the comx extension, you disable mouse-device use on all ports. This switch can be useful for UPS devices because it prevents accidental start of shutdown as a result of port polling.

  • /pcilock. Prevents the hardware abstraction layer (HAL) from reassigning BIOS resources. For more information about /pcilock, see "Ask Dr. Bob," October 2000.

  • The following are triple-boot option switches for NT, Windows 95, and MS-DOS:

  • /win95. Loads bootsec.dos. Instead of loading NT, the system places the Win95 boot option into the hard disk's boot sector.

  • /win95dos. Loads bootsec.w40. Instead of loading NT, the system places the DOS boot option into the hard disk's boot sector.

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