What is _CID?
Quick note explaining _CID for BIOS/UEFI and embedded firmware readers.
What is _CID?
_CID (Compatible ID) is an ACPI object that lists IDs compatible with the device. It helps the OS match a generic or compatible driver when the primary _HID is not enough.
Why it matters
- Helps the OS understand platform devices or resources.
- Connects firmware description with OS driver behavior.
- Useful when debugging ACPI namespace, resource, or table issues.
Practical example
Example: if the OS does not bind a driver to an ACPI device, check _STA, _HID/_CID, and _CRS in that order.
Quick checklist
- Does the object/table appear in the ACPI namespace or OS table dump?
- Do _STA, _HID/_CID, and _CRS report consistent information?
- Do OS logs show ACPI errors or resource conflicts?
Quick takeaway
_CID is the contract between firmware description and OS interpretation.
Related notes
Public references
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