By default, the Desktop, Taskbar, and Explorer run in a single process using multiple threads. To set NT so Taskbar and Desktop will run in one process with each instance of Explorer in a separate process, you can apply the following Windows NT / Windows 2000 Registry hack :

Hive: HKEY_CURRENT_USER
Key: Software\Microsoft\Windows\CurrentVersion\Explorer
Name: DesktopProcess
Type: REG_DWORD
Value: 1 separate process for Explorer
Value: 0 Explorer shares process with Desktop and Taskbar

Each new instance of Windows NT Explorer.exe will get its own thread. If this causes shell problems or for background see Q181562.

Windows 2000's Explorer is particularly optimized for separate thread operation.