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Microsoft states that ACPI_BIOS_ERROR 0xA5 indicates the computer's ACPI BIOS is not fully compliant with the ACPI specification.
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Diagnose 0xA5 ACPI_BIOS_ERROR using parameter 1, ACPI tables, BIOS version, firmware reset and vendor updates.
Microsoft states that ACPI_BIOS_ERROR 0xA5 indicates the computer's ACPI BIOS is not fully compliant with the ACPI specification.
Microsoft's documentation uses Parameter 1 to distinguish many different incompatibility classes.
ACPI provides the contract between firmware and the operating system for power management, device namespace and interrupt routing. 0xA5 means Windows found some ACPI firmware data invalid or non-compliant.
0xA5 is not a single-cause bug check. Microsoft's Parameter 1 distinguishes SCI interrupt resources, method return types, resource descriptors, namespace objects, interrupt routing, FADT/RSDP/XSDT and ACPI-mode initialization classes.
If a minidump exists, WinDbg `!analyze -v` can expose the bug-check parameters. A generic 'update BIOS' answer ignores valuable Parameter 1 information.
Get-ChildItem C:\Windows\Minidump | Sort-Object LastWriteTime -Descending | Select-Object -First 5 Name,Length,LastWriteTimeMicrosoft points users to an updated BIOS because the defect may be in firmware ACPI tables or behavior. Only use official firmware for the exact motherboard or laptop model.
Flashing firmware from a similar model or a modified BIOS creates a much greater brick risk. Record current version, exact model, power state and the vendor's rollback/recovery procedure first.
msinfo32A BIOS/UEFI update can alter TPM measurements and trigger BitLocker recovery. Verify the recovery key and record Secure Boot, VMD and boot settings before updating.
manage-bde -statusmanage-bde -protectors -get C:After CMOS reset or BIOS update, UEFI/Legacy, CSM, VMD/RAID, Secure Boot, OS Type and PCIe settings can revert. Not all are direct ACPI-table errors, but they can change the platform profile seen by Windows.
Do not rely only on 'load defaults'; compare the previously working firmware profile against vendor guidance and saved settings when possible.
In a VM, ACPI_BIOS_ERROR can point to virtual firmware/chipset/hardware-version rather than the physical BIOS. Review Hyper-V generation, VMware virtual hardware version and hypervisor migrations.
| Parameter | Class |
|---|---|
| 0x01 | SCI resource / interrupt information |
| 0x0F | Resource descriptor parsing problem |
| 0x11 | ACPI mode initialization subcauses |
Do not use destructive boot, BitLocker, firmware, partition or storage commands without backups and a rollback plan. Never copy example drive letters without verification.
Not if the firmware is genuinely ACPI-incompatible.
First check whether the vendor has a newer firmware and which 0xA5 parameter is present.
For boot, storage, RDP or update problems on a Windows VPS or physical server, send the exact error code, Windows version and console screenshot to technical support.