How to Access 64-Bit and 32-Bit Registry Keys from a 32-Bit Application?

Accessing the 64-bit Registry from a 32-bit Application

Thanks to WOW64 (Windows on Windows 64-bit), 32-bit applications can access the 64-bit registry. This subsystem facilitates 64-bit access within the 32-bit environment.

Accessing the 64-Bit Registry Key

Use RegistryView.Registry64 to access the 64-bit registry:

using Microsoft.Win32;

string value64 = string.Empty;
RegistryKey localKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
localKey = localKey.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
if (localKey != null)
{
    value64 = localKey.GetValue("RegisteredOrganization").ToString();
    localKey.Close();
}
Console.WriteLine($"RegisteredOrganization [64-bit]: {value64}");

Accessing the 32-Bit Registry Key

Use RegistryView.Registry32 to access the 32-bit registry:

string value32 = string.Empty;
RegistryKey localKey32 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32);
localKey32 = localKey32.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion");
if (localKey32 != null)
{
    value32 = localKey32.GetValue("RegisteredOrganization").ToString();
    localKey32.Close();
}
Console.WriteLine($"RegisteredOrganization [32-bit]: {value32}");

Important Considerations: WOW64, Registry Paths, and Key Queries

• On 64-bit Windows, HKEY_LOCAL_MACHINESoftwareWow6432Node holds values used by 32-bit apps.
• Both 32-bit and 64-bit applications access HKEY_LOCAL_MACHINESoftware as expected due to WOW64 redirection.
• HKEY_LOCAL_MACHINESoftwareWow6432Node is absent in older Windows versions and 32-bit Windows 7.

To retrieve values from both 64-bit and 32-bit registries (useful for scenarios like retrieving SQL instance names), a union query is recommended:

public static IEnumerable<string> GetAllRegValueNames(string regPath, RegistryHive hive = RegistryHive.LocalMachine)
{
    var reg64 = GetRegValueNames(RegistryView.Registry64, regPath, hive);
    var reg32 = GetRegValueNames(RegistryView.Registry32, regPath, hive);
    var result = (reg64 != null && reg32 != null) ? reg64.Union(reg32) : (reg64 ?? reg32);
    return (result ?? new List<string>().AsEnumerable()).OrderBy(x => x);
}

This provides a consolidated view of registry values, regardless of the application's architecture.

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