If you use the /3GB switch in the Boot.ini file to support a program that can use more than 2 GB of virtual address space, a driver may not be loaded when Windows starts. This is more likely to occur with video adapter drivers. This is especially likely to occur if the hardware device contains a lot of onboard random access memory (RAM) that is used as a buffer.

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This problem occurs because the driver is trying to reserve a large block of contiguous virtual memory addresses in the kernel address space to map the device's buffer. When you are use the /3GB switch, the memory that is available to the kernel is halved. The kernel might not be able to allocate a large enough block of memory to satisfy the driver's request.

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To resolve this problem, obtain the latest service pack for Windows XP. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

File information

The English version of this fix should have the following file attributes or later:

   Date         Time   Version      Size      File name
   -------------------------------------------------------
   10-Jun-2002  15:44  5.1.2600.48  1,836 KB  Ntoskrnl.exe
   10-Jun-2002  15:44  5.1.2600.48  1,804 KB  Ntkrnlmp.exe
   10-Jun-2002  15:44  5.1.2600.48  1,858 KB  Ntkrnlpa.exe
   10-Jun-2002  15:44  5.1.2600.48  1,831 KB  Ntkrpamp.exe
				

After you install this hotfix, you can use the new /USERVA memory-management switch. You can use this switch to tune the memory that is allocated above 2 GB to User mode and taken from the kernel. By doing this, you can find a number that permits the driver to be loaded.

For example, using the /USERVA=2800 switch in the Boot.ini file configures a User mode virtual address space of 2800 MB and a Kernel mode virtual address space of 1196 MB.

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows XP Service Pack 1.

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For more information about using the /USERVA switch, see the following Microsoft Knowledge Base article:

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