Jean-Francois Baril has a complicated problem to solve:
I need to have two monitors that mirror my iMac display, so that I can buy one iMac and use it in three different adjacent rooms (in a doctor’s office).
Baril wonders if display mirroring would solve the problem.
Yes! Any iMac model with two Thunderbolt ports can support one monitor via each port using the DisplayPort video standard, which uses the same connector type and passes over the Thunderbolt standard.
You’ll also need to think about what resolution displays you want to use. You can get an 21.5-inch iMac either standard 1080p resolution (1920×1080 pixels) or 4K (4096×2304 pixels), or the 27-inch iMac with 5K (5120×2880 pixels). The 21.5-inch models can handle two 1080p displays (or thereabouts), while the 5K iMac can support two 4K monitors.
Depending on how close the other rooms are and how much you can drill through a wall or run cords over a partition, you will probably need longer than a typical DisplayPort cable, which is normally about 6 feet (2 meters) or shorter. Affordable, longer DisplayPort cables can’t carry 4K, which isn’t an issue for any but the 27-inch iMac. But keep that in mind. Monoprice has a 15-foot Mini DisplayPort to HDMI cable for $16. (Most DisplayPort capable monitors will also have an HDMI port.)
If you need longer distances or want 4K from a 27-inch iMac, it’s possible, but you’ll spend several hundred dollars, as you have to leap to high-end ethernet style or fiber-optic cabling with converters.
Next, you can set up mirroring, so that both external displays mirror the internal one. Apple has detailed instructions about enabling mirroring and Option-dragging displays onto the main one. Because your external displays will be lower resolution, OS X will figure out the lowest compatible dimensions among all the monitors connected.
Finally, you need keyboards and mice or trackpads. Bluetooth is your best bet, as most keyboards support a signal-strength flavor that carries about 30 or so feet (10 meters), reducing by walls and other obstacles. I’d make sure the keyboard and pointing device used with the main Mac is plugged in via USB, because Bluetooth can only support 7 devices at a time, and Apple recommends using only 3 or 4 at once.
Of course, with keyboards and displays in different rooms, you’ll have to make sure that multiple people aren’t trying to use the same computer at once. It’s still just a single session you’re working with mirrored across multiple displays. You could find yourself confused when you struggle to move the mouse pointer onscreen as it keeps getting dragged elsewhere.
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