"ACPI BIOS is attempting to write to an illegal IO port address" error message when you open the event viewer

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Article ID: 283649 - View products that this article applies to.
This article was previously published under Q283649
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The following error message may be in the system event log when you open the event viewer:
Source: ACPI Category: None Type: Error Event ID: 5 User: N/A Computer: Machine_Name Description: AMLI: ACPI BIOS is attempting to write to an illegal IO port address (0xnnnn), which lies in the 0xXXXX - 0xYYYY protected address range. This could lead to system instability. Please contact your system vendor for technical assistance.

For more information, see Help and Support Center at:
Where nnnn is one of the following:
   Address or Range   Description
   0x000 – 0x009      ISA DMA
   0x020 – 0x021      PIC
   0x040 – 0x043      Timer1, Refresh, Speaker, Control Word
   0x048 – 0x04B      Timer2, Failsafe
   0x070 – 0x071      CMOS/NMI enable
   0x074 – 0x076      Extended CMOS
   0x081 – 0x083      DMA
   0x087              DMA
   0x089              DMA
   0x08A – 0x08B      DMA
   0x08F              DMA
   0x090 – 0x091      Arbitration Control Port, Card Select Feedback
   0x093 – 0x094      Reserved, System board setup
   0x096 – 0x097      POS channel select
   0x0A0 – 0x0A1      Cascaded PIC
   0x0C0 – 0x0DF      ISA DMA
   0x4D0 – 0x4D1      Edge, level control registers for PIC 
   0xCF8 – 0xCFF      PCI Configuration Space Access Pair


This behavior may occur if your computer's basic input/output system (BIOS) tries to write to one of the earlier ports by using an AML [Advanced Configuration and Power Interface (ACPI) Machine Language] System IO operation region. Your try may be blocked by Microsoft Windows XP because accessing these ports by using this mechanism is considered dangerous and can cause system instability. This feature is designed to improve the stability of your computer's operating system.


This behavior is by design.


Contact the BIOS vendor for a possible BIOS update. For more information, visit the following Microsoft Web site:


Article ID: 283649 - Last Review: September 22, 2006 - Revision: 3.2
  • Microsoft Windows XP Professional
  • Microsoft Windows XP Home Edition
kburl kbeventlog kbevent kberrmsg kbhardware kbprb KB283649

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