I use Windows. (I have Windows 7 now, having previously used XP until a few weeks after support for it was withdrawn by Microsoft, and I’m resisting upgrading to Windows 10 until they withdraw support for Windows 7. I won’t use Windows 8.)
I have one screen only (I think it’s probably 24" - they’re measured diagonally, aren’t they?).
I’ve never wanted a second screen. I know many traders have multiple screens but I’ve never seen the point, for myself, because I think it’s less effort to click on a Window tab than it is to have to look in a different direction. I can only look at one at a time, so I do everything on one screen: a few trading-chart windows, my online backgammon games (which give me something to do between trades and keep me patient while waiting for them to materialise) and the BBC iPlayer so I can watch (or at least listen to) [I]The Daily Politics[/I] every day, and all those BBC2 and BBC4 documentaries - anything non-fiction, that I can treat more or less like the radio and not have to concentrate when I don’t want to, or look at the picture-screen very often. When I’m not playing CD’s, that is. I do have a high-powered PC to run it all at once (an Intel “i7 chip”, whatever that means) and very high-speed cable internet.
I can trade from my laptop, if necessary, and I sometimes do when I’m (actually quite often) away from home for many weeks at a time, but it’s not as comfortable as a bigger screen.