I believe it depends on the computer. If I remember correctly, @Woland has an Intel GPU in his laptop and it works for three. I have an AMD in mine, and I can only get two. But the bottom line is that I don't have hard facts on this. Maybe someone else has an idea?
Best Wishes, Mark
Media Artist & Creator of Isadora
Macintosh SE-30, 32 Mb RAM, MacOS 7.6, Dual Floppy Drives