How to switch back and forth between one screen and two

I have my iMac linked up to two monitors. I use both screens only when I want to run Windows, so that I can continue to use Mac without losing screen estate. How do I switch off the other screen when I don't need it? And switch it on again when I do? Most of the time, I prefer just one screen. I noticed that it seems to be a little slower with both screens on.

Your computer shouldn't be slower, unless it's an older model with a slower graphics card or something. When I don't want my second monitor on, I "Turn off mirroring" and shut the external monitor off. If you go into System Preferences>Displays, you can choose to "Show displays in menu bar", where you can easily switch mirroring off and on.

Many thanks, oneironaut. I didn't realise that "mirroring" means having two screens. I thought it meant showing the same content in both screens. Why can't they use a simple phrase like two screens or allow us to select the screens we want to display, something more easily understood. I found that just switching off my other monitor automatically switches off mirroring. But I didn't know if the other screen was switched off and just blank - e.g. will my cursor disappear into the other screen while I try to look for it, .

The slowing down of my computer could be just my imagination, haha.

Mirroring does mean having the same content on both screens at the same time. I'm not sure that there is a really easy way to do what you want to do. The best option I can think of at the moment, since you only use the second screen when running Windows, is to disconnect the monitor when it is not in use.

BTW if you simply turn the power off on the second monitor the cursor will disappear onto it any time the cursor crosses the boundary from one screen to another.

Hi Slydude, many thanks for clarifying. Disconnecting the second screen seems too much work, . Although the cursor does indeed disappear into the blank 2nd screen at the moment (I switched off the 2nd screen), a bit of jiggling brings it back, so I can live with that. Ideally, I'd like to be able to turn on and off the 2nd screen from the Display tool that I have now activated on the menubar. Thanks again.

Your welcome. I should have mentioned that the cursor comes back immediately upon crossing over to the active screen.