Use an old laptop as a monitor? [duplicate]

"You can also enable the built-in external monitor or projector on your host laptop. Then install RealVNC Server on the host and Real VNC Viewer on the remote. Configure RealVNC server via registry to only serve the extended display of the host laptop. Then connect via RealVNC viewer and the remote laptop will display the RealVNC served extended display and the host laptop will display it's normal primary display.

You will need to research RealVNC documentation to edit the registry but the key is adding ""DisplayDevice"", REG_SZ, ""\.\displayX"" to the RealVNC registry setting where X represents the monitor number as identified through the OS display configuration panel. There are also ways to do this from the command line.

I have done this with WIN7 Ultimate 32 and RealVNC Free. I'm actually using this configuration now with an HP DV7-1245DX as host and a HP DV-2116WM as remote extended display. Both laptops are running Win7 Ultimate 32 are networked via WIFI.

MaxiVista software is the easiest to implement and provides the best performance in my limited experience but it is not free. I used MaxiVista for many years with 4 monitors using XP Pro. I'm still looking for other free alternatives with better performance.

Regards."