3.1.4.2 Drive Letter Protocol Events
The server MUST monitor the Windows registry key HKCU\Software\Microsoft\Terminal Server\[session id]\Drive Letter Cache for changes (where [session id] is the decimal RDP session ID). When the key changes, all DWORD Registry Values contained in the key MUST be enumerated and the value name/DWORD value pairs are stored packed into a single contiguous block, which is then sent to the RDP client using a SADLE_SerializedCache message.