Event ID 1801 may be logged in the System log on a computer that is running Windows Vista

A computer that is running Windows Vista may stop responding. Or, programs that are running on this computer may stop responding. Also, you may receive a Stop error in Windows Vista. Moreover, an event that resembles the following may be logged in the System log:

Source: Application Popup
Event ID: 1801
Level: Error
User: N/A
Text: The hardware has reported an uncorrectable memory error.

The following issues may cause the problems that are mentioned in the "Symptoms" section.

Cause 1

This problem may occur because of physical memory errors.

Cause 2

This problem may occur because of incorrect random access memory (RAM) timing issues in the basic input/output system (BIOS).

Cause 3

This problem may occur because the processor is overclocked.

Cause 4

This problem may occur is memory overwrites direct memory access (DMA).

Note Memory chips that have Parity bits or error-correction coding (ECC) bits also experience memory errors that occur because of the first three causes that are listed in this section.

To detect possible memory problems, Windows Vista performs a consistency check on a subset of all the physical memory pages. When Windows Vista satisfies a memory request by removing a page from the zeroed list, it may first check the page to confirm whether the contents are still completely zero. For performance reasons, this check is not performed on every page. However, sampling is performed on a subset of all the allocations.

If a page that is checked does not consist of all zeros, memory corruption has occurred. The event that is described in the "Symptoms" section is logged in the System log. Then, the memory is rezeroed, and the system continues.

To resolve this problem, find the most likely cause that is described in the Cause section. Then, use the resolution that is appropriate for the cause.

Resolution for Cause 1

Use directed swapping to find the memory chip that is experiencing data loss.

Resolution for Cause 2

Contact the computer vendor for a BIOS update.

Resolution for Cause 3

Change the system configuration to use supported clock frequencies.

Resolution for Cause 4

Remove recently-added hardware or drivers that may be causing the problem.

The following is the raw data from the event that is described in the "Symptoms" section: The following registry subkeys influence the behavior of the code that checks for memory consistency:

• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PageValidationFrequency
  
  The following is an explanation of the values that you can set for the PageValidationFrequency registry entry:
  • A value of 0 means to check every page.
  • A value of 1 means to check every other page.
  • A value of 2 means to check every fourth page.
  Note Internally, the value is converted to a power of 2.
  
  The default value of the PageValidationFrequency registry entry is 0x10 (decimal 16).
• HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PageValidationAction
  
  The following is an explanation of the values that you can set for the PageValidationAction registry entry:
  • A value of 1 indicates that a stop is initiated when an error occurs.
  • A value of 0 indicates that an event is logged and the operating system continues working.
  The default value of the PageValidationAction registry entry is 0.