The Browser system consists of two components:
The Browser service is the user-mode portion that is responsible for maintaining the browse list, remotely making API calls, and managing the various roles a browser can have. It resides within the LanmanServer service (\systemroot\SYSTEM32\SERVICES.EXE) and is supported by \systemroot\SYSTEM32\BROWSER.DLL. The browser's registry entries are under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Browser key.
The datagram receiver is the kernel-mode portion of the browser, and is simply a datagram and mailslot receiver. It receives directed and broadcast datagrams of interest to the workstation and server services. It provides kernel-level support for the NetServerEnum API, as well as support for remote mailslot reception (second-class datagram-based mailslot messages) and the request announcement services.
The datagram receiver file is \systemroot\SYSTEM32\BROWSER.SYS. The datagram receiver's registry entries are in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DGRcvr key.