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I read out the MSDN about using Multiple Desktop with Windows. MSDN says that Multiple Desktops can be iomplemented Using CreateDesktop()and SwitchDesktop() functions. But it also menions that they are supported ONLY for Windows NT based OS, namely Win2000,Win XP and WinNT.
Platform SDK with MSDN also has an Example of it in the folder ..sample\vc\sdk\sdktools\winnt\switcher.
I wanted to know how do some commercially available software like Virtual Desktop allow such multiple desktops for Windows 9x based OS?
???

Easy: windows on another desktop are kept hidden, and windows on the current desktop are allowed to be shown. To switch desktops, hide all the current windows, and show all the windows in the other desktop that should be visible.

Native multiple desktop support in NT makes this much more efficient, since the OS doesn't need to loop through all windows, showing and hiding them. In fact, the screen you see when you press Ctrl+Alt+Del is another desktop, as is the screen saver. Switching to either of these is almost instant.

the light house shell for windows implements this concept.

You might check out PowerToys for Windows XP...

Just like Tim said nativity makes things more easier on Windows NT.
Windows 9x based multiple desktops aplicatiopns have a lot to do inside code for this switching. One application, "Virtual Desktop", I saw implemented the same using COM.

Hey all these musing made me think is there the multiple logon,(u can log to different accounts simultaneously) found in Windows XP possible on Windows 2000 or 98. ???