BOOT.INI Option Reference
Copyright © 1996-1999 Mark Russinovich
Last Updated August 4, 1999
There are number of BOOT.INI switches that are useful for driver developers that wish to test
their drivers under a variety of different system configurations without having to have a separate
machine for every one. For example, limiting the amount of memory NT sees can be useful for
stressing memory loads, and limiting the number of processors for testing scalability. I've
compiled a complete list of the options that BOOT.INI currently supports. Switches new to Win2K
(NT 5) are in red, and are present in some Beta builds but may not appear in the final release.
/PAE
/NOPAE
/NOLOWMEM
/NOGUIBOOT
/FASTDETECT
/BOOTLOG
This has NTLDR load ntkrnlpa.exe, which is the version of the
x86 kernel that is able to take advantage of Intel Physical
Address Extensions (PAE), even when a system doesn't have
more than 4GB of physical memory. PAE permits an x86 sytem to
have up to 64GB of physical memory, but an operating system
must be specially coded to use memory beyond 4GB (the
standard x86 limit). The PAE-version of the Win2K kernel
presents 64-bit physical addresses to device drivers, so this
switch is helpful for testing device driver support for large memory
systems.
This switch forces NTLDR to load the non-PAE version of the
Win2K kernel, even if the system is detected as supporting x86
Physical Address Extensions (PAE) and has more than 4GB of
physical memory.
This switch requires that the /PAE switch be present and that the
system have more than 4GB of physical memory. If these
conditions hold, then the PAE-enabled version of the Win2K
kernel, ntkrnlpa.exe, will not use the first 4GB of physical
memory. Instead, it will load all applications and device drivers,
and allocate all memory pools, from above that boundary. This
switch is useful only to test device driver compatability with large
memory systems.
When this option is specified the VGA video driver responsible for
presenting bit mapped graphics during Win2K's boot process is
not initialized. The driver is used to display boot progress
information, as well as to print the Blue Screen crash screen, so
disabling it will disable Win2K's ability to do those things as well.
When you dual boot NT 4.0 and Win2K the Win2K version of
NTDETECT.COM is used during the boot process. In Win2K
detection of parallel and serial devices is performed by plug-andplay device drivers, but NT 4.0 expects NTDETECT to perform
the detection. Thus, specifying FASTDETECT causes
NTDETECT to skip parallel and serial device enumeration for a
boot into Win2K, whereas ommitting the switch has NTDETECT
perform enumeration for a boot into NT 4.0. Win2K setup
automatically recognizes dual-boot configurations and sets this
switch for BOOT.INI lines that specify a Win2K boot.
Specifying this switch will result in NT writing a log of the boot to
the file %SystemRoot%\NTBTLOG.TXT. The log has entries that
detail which drivers load and do not load during the boot process.
Here is example output from a log (note that the log file is un
UNICODE):
Microsoft (R)
Loaded driver
Loaded driver
Loaded driver
Loaded driver
Loaded driver
Loaded driver
...
/SAFEBOOT:
Windows NT (R) Version 5.0
\WINNT\System32\ntoskrnl.exe
\WINNT\System32\hal.dll
\WINNT\System32\BOOTVID.dll
pci.sys
isapnp.sys
intelide.sys
You should never have to specify this option manually, since
NTLDR does it for you when you use the F8 menu to perform a
safe boot. Following the colon in the option you must specify one
of three additional switches: MINIMAL, NETWORK, or
DSREPAIR. The MINIMAL and NETWORK flags correspond to
safe boot with no network and safe boot with network support. A
safe boot is a boot where NT only loads drivers and services that
are specified by name or group in the Minimal or Network
Registry keys under
HKLM\System\CurrentControlSet\Control\SafeBoot. The
DSREPAIR (Directory Services Repair) switch causes NT to boot
into a mode where it restores the Active Directory from a backup
medium you present.
An additional option that you can append is
"(ALTERNATESHELL)". This tells NT to use the program
specified by
HKLM\System\CurrentControlSet\SafeBoot\AlternateShell as the
graphical shell, rather than to use the default which is Explorer.
/PERFMEM=
/PERFPAGES=
These flags are not likely to be supported in the final release of
Windows 2K, as they are used to have NT reserve physical
memory for the purposes of Basic Block Testing (BBT). There is
only one reference I've been able to find BBT: the transcript
(posted at Microsoft's web site) of the US vs. Microsoft trial from
February 2, 1999. In the transcript Jim Allchin is on the stand and
responds to questions about BBT by DOJ attorney David Boies,
saying that it is a performance optimizing system Microsoft uses
on code before releases in order to minimize their paging
footprints.
PERFMEM specifies the physical memory to reserve in MB, and
PERFPAGES in number of pages - they should not be specified
together. A pointer to the reserved BBT buffer is inserted in the
Thread Environment Block (TEB) of every thread, but there
appears to be no other references to the buffer in Beta 3.
/INTAFFINITY
This new switch directs the multiprocessor HAL (HALMPS.DLL)
to set interrupt affinities such that only the highest numbered
processor in an SMP will receive interrupts. Without the switch
the HAL defaults to its normal behavior of letting all processors
receive interrupts.
/MAXPROCSPERCLUSTER= It seems that the multiprocessor HAL in Win2K (HALMPS.DLL)
has the ability to work with multiprocessors that are made up of
/TIMERES=
tightly-coupled clusters of smaller multiprocessors. For example,
if you had an 8-way system that was made up of 2 4-way
clusters, the processor IDs of each processor would have to be
specified in a cluster-oriented manner by the HAL. The maximum
cluster size is 4 and the default is 0 (system is not based on
clusters). Example: /MAXPROCSPERCLUSTER=3.
On the multiprocessor HAL (HALMPS.DLL) this option will set the
resolution of the system timer. The argument is a number
interpreted in 100's of nanoseconds, but the rate will be set to the
closest resolution the HAL supports that is not larger than the one
requested. The HAL supports the following resolutions:
100's of
milliseconds
nanoseconds
/YEAR=
/CLKLVL
/USE8254
/MAXMEM=
/BURNMEMORY=
/ONECPU
/NUMPROC=
/SOS
9766
.98
19532
2.0
39063
3.9
78125
7.8
The default resolution is 7.8ms. The system timer resolution
affects the resolution of waitable timers. Example:
/TIMERES=9000 would set the timer to a resolution of .98ms.
This option is obviously present for Y2K testing. Specifying it
causes NT core time function to ignore the year that the
computer's real-time clock reports and instead use the one
indicated. Thus, the year used in the switch affects every piece of
software on the system, including the NT kernel. Example:
/YEAR=2001. Note: this option is only available on NT 4.0
Service Pack 4 and Windows 2000.
Has the Multiprocessor x86 HAL (HALMPS.DLL) configure itself
for a level-sensitive system clock, rather then an edge-triggered
clock.
This switch is intended for systems with older BIOS's. It instructs
the NT HAL to use the 8254 timer chip as its base timer. See
Microsoft KB Article Q169901 for more information.
This option will limit NT to using only the amount of memory you
specify. The number is interpreted as MB. Example:
/MAXMEM=16 would limit NT to using 16MB of the system's
memory.
This option will cause NT to "forget" about the amount of memory
specified, which limits memory like /MAXMEM. The value
specified is interpreted as MB. Example: /BURNMEMORY=128
would have NT discard 128MB of the physical memory on the
machine as unusable.
This option will have NT only enable one CPU of a multiprocessor
system.
Only the number of CPUs specified will be enabled. Example:
/NUMPROC=2 on a 4-way system will cause 2 of the 4
processors to be unused by NT.
Causes NT to print information about what drivers are being
loaded as the system boots.
/BASEVIDEO
/NODEBUG
/CRASHDEBUG
/DEBUG
/DEBUGPORT=
/BAUDRATE=
/BREAK
/KERNEL=
/HAL=
Causes NT to use the standard VGA display driver when moving
to GUI mode.
Prevents kernel-mode debugging from being initialized. Overrides
the specification of any of the three debug-related switches,
/DEBUG, /DEBUGPORT and /BAUDRATE.
If you include this switch, the kernel debugger is loaded when the
system boots, but remains inactive unless a crash occurs. This
allows the COM port that you specify (or COM1 by default) to be
available for other use while the system is running.
Enables kernel-mode debugging.
Enables kernel-mode debugging and specifies an override for the
default serial port (COM1) to which a remote debugee is
connected. Example: /DEBUGPORT=COM2.
Enables kernel-mode debugging and specifies an override for the
default baud rate (19200) at which a remote debugee will
connect. Example: /BAUDRATE=115200.
Causes the HAL to stop at a breakpoint at HAL initialization. The
first thing that the NT kernel does when it initializes is to initialize
the HAL, so this breakpoint is the earliest one possible. The HAL
will wait indefinitely at the breakpoint until a debugger connection
is made. If the switch is used without the /DEBUG switch the
system will Blue Screen with STOP code of 0x00000078
(PHASE0_EXCEPTION).
These options specify overrides of NTLDR's selection of the file
named NTOSKRNL.EXE in the system root (<winnt>\system32)
as the kernel's image file and of the file named HAL.DLL as the
HAL image file. They are extremely useful for alternating between
a checked kernel environment and a free kernel environment. If
you wish to boot into a checked environment that consists solely
of the checked kernel and HAL, which is typically all that is
needed to test drivers, follow these steps on a system installed
with the free build (retail NT):
1. Copy the checked version of the kernel from the checked
build distribution CD to your <winnt>\system32 directory,
naming it NTOSKCHK.EXE. If you are on a uniprocessor
then copy NTOSKRNL.EXE, otherwise copy
NTKRNLMP.EXE.
2. Copy the checked version of the HAL from the checked
build distribution CD to your <winnt>\system32 directory,
naming it HALCHK.DLL. To determine which HAL to copy,
go into your <winnt>\repair directory and open setup.log in
Notepad. Search for HAL.DLL and you'll find a line like
"\WINNTF\system32\hal.dll="halmps.dll","1a01c". The name
to the right of the equal sign is the name of the HAL you
should copy.
3. Make a copy of the default line in the system's BOOT.INI.
4. In the string description of the boot selection add
something that indicates that the new selection will be for a
checked build environment e.g. "Windows NT Server Version
4.0 CHECKED".
5. Add the following to the end of the new selection's line:
/KERNEL=NTOSKCHK.EXE /HAL=HALCHK.DLL
You're done. Now you can select the new line to boot into a
checked environment or select the pre-existing selection to boot
into the free build.
/3GB
/WIN95
/WIN95DOS
/PCILOCK
/NOSERIALMICE=[COMx |
COMx,y,z...]
/SCSIORDINAL:
This switch made its debut in NT 4.0 Service Pack 3 and is
supported on all later releases of NT. It will cause the split
between the user and system portions of NT's virtual address
map to move from 2GB user, 2GB system to 3GB user, 1GB
system. Giving virtual memory intensive applications like
database servers a larger address space can improve their
performance. Note, however that for an application to take
advantage of this feature two additional conditions must hold: The
system must be part of the NT Enterprise suite (SP3 is not) and
the application must be flagged as a 3GB-aware application. See
Microsoft KB Article Q171793 for additional information.
This switch is only pertinent on a triple-boot system that has
DOS, Win9x and Windows NT installed. Specifying the /WIN95
switch directs NTLDR to boot the Win9x boot sector stored in
BOOTSECT.W40. See Microsoft KB Article Q157992 for more
information.
This switch is only pertinent on a triple-boot system that has
DOS, Win9x and Windows NT installed. Specifying the
/WIN95DOS switch directs NTLDR to boot the DOS boot sector
stored in BOOTSECT.DOS. See Microsoft KB Article Q157992
for more information.
Stops Windows NT from dynamically assigning IO/IRQ resources
to PCI devices and leaves the devices configured by the BIOS.
See Microsoft KB Article Q148501 for more information.
Disables serial mouse detection of the specified COM port(s).
Use this switch if you have a component other than a mouse
attached to a serial port during the startup sequence. If you use
/NOSERIALMICE without specifying a COM port, serial mouse
detection is disabled on all COM ports. See Microsoft KB Article
Q131976 for more information.
Adding a new SCSI device to a system with an on-board SCSI
controller can cause the controller's SCSI ID to change, so you
use this switch to direct NT to the SCSI ID of the controller. See
Microsoft KB Article Q103625 for more information.
Thanks to Jonas Fischer for pointing out the PCILOCK and NOSERIALMICE switches. Thanks to
Rob Green for information on the FASTDETECT switch.