How many displays are possible on a Mac?

6 August 2015, 07:29

I wrote a brief feature for MacWorld about connecting more than one external display to a Mac.

It got me thinking: How many screens can I feasibly attach to a Mac without the need for special hardware — such as the Matrox or Diamond adapters discussed in the article?

On my MacBook Pro 15in I can run two external displays via the two Thunderbolt sockets. That makes a total of three displays: the Macbook’s built-in display, and two others. (For what it’s worth I didn’t use Thunderbolt displays but instead used Thunderbolt-to-DVI and Thunderbolt-to-VGA adapters, which work just fine.)

Then I used the Duet app to turn my iPad into a fourth display. I would’ve liked to connect my iPhone as an external display in addition, using Duet, but Duet currently only lets you run one iOS device as an external display. I guess the clue is in the title of the app…

Hmmm… Pretty good going so far. But what about using an Apple TV to create a fifth desktop on a TV via AirPlay? This would never be very usable because AirPlay to an Apple TV brings a certain amount of lag, but it could be used for something like an email app.

Sadly, this didn’t work. Switching on the Apple TV via the menubar icon caused a lot of flickering — all the displays switching on and off — and somehow display mirroring gets activated. I was unable to turn off mirroring and also keep AirPlay activated — turning it off also turned off AirPlay.

Here are some things I noticed when running a lot of displays:

  1. There’s a lot of mouse “ramping” to get the cursor from one display to another. It makes you realise that the WIMP environment was built for one display, and two at most.
  2. It’s very easy to lose the mouse cursor. OS X El Cap will help fix this with its clever cursor-revealing trick.
  3. All the screens have different colour and brightness balances, and calibration is a nightmare. In a perfect world you would have to (a) find a screen that matches the internal display’s colour balance, even if that’s just a rough match, and (b) use only those displays for external screens. As it is, the screen I’m running to the left of the MacBook Pro is slightly warmer in colour than the MacBook, while the screen to the right of the laptop is positively yellow by comparison. Both displays would look OK in isolation.

Know better?