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TL;DR

As far as I know there is no way to easily disable/enable an iMac's internal display at will while simultaneously powering up an external display. Can anyone suggest a solution to achieve this functionality?

Background

Here's the use case scenario presented to me today:

This user basically wants a 21" or 27" laptop that will power two external 27" displays for 3 out of every 4 weeks. For the remaining week it needs to be on the road with them. As no such laptop exists, the scenario is that they want to use an iMac as a tower under a desk for 3 weeks each month. The iMac would provide all the CPU/GPU processing power to run applications and power the two 27" displays. Then, when they need to go on the road, they would just grab the iMac and cart it around in a car. Their desk already has two 27" displays (connected to monitor arms), and therefore it is not practical to just move one of the displays for 3 weeks of the month, nor is there the room to also place an iMac on the desk.

I did ask Why not just get a 15" MBP, but was told they need at least a 21" screen (preferably more) to display the data they work with.

The only practical solutions I could come up with were:

  • Use two Macs - an iMac to take on the road, and another suitable Mac (perhaps a current model Mac Pro or 15" MBP) to keep on the desk. However, they were not keen on this solution as the data is highly sensitive and it increases the risk of a breach. Apparently the data is so sensitive that the computer will never be connected to the internet and it will be secured in a custom-built cage below the desk. I did ask how they intend to manage the risk on a device that is on the road for one week each month, but was told that was out of scope!

  • Turn the built-in display brightness down to zero - The user is concerned about the long-term impact this will have on the display etc as the display is not actually disabled or put to sleep while it's being used in this fashion for 3 weeks each month.

My hope is that I'm just missing something really simple (e.g. a terminal command that works on a desktop Mac to put the built-in display to sleep), or a piece of software that does the same thing. Any suggestions/hacks/workarounds are most welcome!

  • When you plug an external display into any (non AIO) computer, how do you disable the display? – Allan Jun 12 '17 at 11:20
  • I'm not sure I follow you (I must be having one of those days I think), but on a non AIO computer there is no internal display to disable. But, why do I think you're trying to make a point? :) Like I said, I'm sure I'm missing something obvious here. – Monomeeth Jun 12 '17 at 11:30
  • An internal display is nothing special. It's just "hard" connected via an LVDS connector and to power via direct connection to a power supply with no power switch. So my question is more illustrative in nature - if you have an external display connected and on, how would you disable it from the system? The answer is the same for the internal display. I don't know of any way to disable a connected and powered display. – Allan Jun 12 '17 at 11:35
  • Ah, of course :) But I was looking for a practical solution. LOL Even on an older iMac with only magnets and screws to navigate, it'd be a PITA to disconnect/reconnect the LVDS on a regular basis. (I known you were just illustrating a point). He should just change his setup so that it's a 27" iMac on the desk and one 27" external display. TBH, I'm not entirely comfortable with the idea of an iMac being carted around in a car for one week in every four. I suspect it's a recipe for disaster. – Monomeeth Jun 12 '17 at 11:41
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    These use case scenarios are what baffle me...instead of buying the right tool for the job (a Mac mini for example) they opt for an AIO then proceed to change its defining characteristics. This is like buying a pickup truck but wanting to "disable" the bed portion because what they really need and want is a car. – Allan Jun 12 '17 at 11:46

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