Windows App Compatibility Shims Registry Path

The Windows Application Compatibility (AppCompat) engine uses specific registry keys to manage, register, and apply compatibility shims across the operating system. This guide details the exact system-wide Windows Registry paths used to store installed Shim Databases (SDB files), active compatibility layer flags, and custom runtime configurations applied to legacy applications.

Primary System-Wide Registry Path

The central registry location for system-wide application compatibility settings is located under the Local Machine hive at:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags

Key Subkeys and Their Functions

Within the AppCompatFlags branch, Windows organizes compatibility shims into distinct subkeys depending on how the fix is applied:

• Compatibility Layers (\Layers): HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers This key contains system-wide compatibility mode settings (such as running an app in Windows 7 compatibility mode or as an Administrator) applied to all users. The string value names correspond to the absolute path of the target executable, while the value data contains the specific layer flag (e.g., ~ WIN7RTM or ~ RUNASADMIN).

• Installed Shim Databases (\InstalledSDB): HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\InstalledSDB This subkey registers all installed custom or system shim database (.sdb) files using their unique Globally Unique Identifiers (GUIDs). Each subkey here points to the physical file location and registration metadata created when databases are installed via the sdbinst.exe utility.

• Custom Shims (\Custom): HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Custom This path maintains mappings between specific executables and custom SDB identifiers to ensure the correct shim definitions are loaded upon application launch.

32-Bit Applications on 64-Bit Windows (WOW64)

For 32-bit applications running on a 64-bit version of Windows, the operating system mirrors these settings under the WOW6432Node registry hive:

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows NT\CurrentVersion\AppCompatFlags

This ensures that 32-bit processes interacting with the Windows registry can resolve installed shim databases and compatibility layers seamlessly.