Monday, March 4, 2024

M3 MacBook Pro Multi-Display Support via Software Update

Zac Hall:

Both the M3 MacBook Air and the M3 MacBook Pro offer support for one external display with up to 6K resolution at 60Hz when the display is open, and with the update, the M3 MacBooks will also be able to power two 5K external displays with a resolution of up to 60Hz. That is equivalent to the Studio Display, so users can expect to be able to run two of Apple’s 5K displays in clamshell mode.


Apple has confirmed to 9to5Mac that a software update for the 14-inch MacBook Pro will gain the ability to drive two external displays with the lid closed. The feature will work identically to how it works with the new M3 MacBook Air.


One external display with up to 6K resolution at 60Hz

Close the MacBook Air lid to use a second external display with up to 5K resolution at 60Hz

So I think this means you can have one external 6K and one external 5K.

Juli Clover:

The higher-end M3 Pro and M3 Max MacBook Pro models are already able to drive multiple displays, so this change only applies to the 14-inch MacBook Pro that has the M3 chip. This machine replaced the prior-generation 13-inch MacBook Pro, which Apple has now done away with.

Mr. Macintosh:

The M2 Mac mini can support 2 monitors. Was 2 monitor support (for laptops) built into the M3 chip? If not, can the M2 & M1 also run 2 monitors with a software update?

Joe Rosensteel:

It is interesting that this is something that could be controlled in software … all this time … and won’t come to the M1 or M2 machines. I wonder what discussions happened to get this concession. Did the dings in reviews matter? Product returns? Qualtrics surveys?

Matt Birchler:

I have no idea how it is in the wider world, but IT at my work has been hit up by nearly every person who was issued a an M1/M2 device asking why they can’t get both their monitors to work. “Even my crappy Dell could do it,” is not an uncommon reaction when they’re told what’s up.


Update (2024-03-07): Eric Schwarz:

In my day job, I see plenty of lower-end business PC laptops connected to USB-C docking stations driving dual 1080p monitors, yet it requires a much more expensive Mac to do the same thing. While an M1 MacBook Air probably doesn’t have the horsepower to drive dual 5K monitors, I think if two external displays work with the internal one off or lid closed, this is something Apple should bring to all their Apple Silicon-based MacBooks. If the M1 Mac mini could do that why not open it up to other Macs?

Update (2024-03-08): Hector Martin:

Apple introduced this capability into the M2 already. It’s why the M2 Mac Mini supports two displays over Type C/Thunderbolt, while the original M1 Mac Mini does not, and requires one display to be on HDMI. The laptops are logically equivalent to a Mac Mini with the HDMI port hardwired to the internal panel.

The only reason this wasn’t enabled on M2 laptops so far is that it requires extra firmware support to disable the internal panel and reconfigure the primary display pipe for external mode. The firmware has lots of special support for the internal panel, so it’s not “just” another screen connected to the system, and there’s a lot of stuff that has to be done properly to make this work as intended.

Now the question is whether Apple will backport this to M2 or not. DCP firmware nominally has an identical interface synced between all platforms, so it should be a common codebase, so it should be easy to do. But they might explicitly lock it out, because I suspect Apple have a habit of not wanting to admit something was unavailable on a given machine due to software/firmware not being ready on time, and they’d rather just pretend its not supported…


Technical details: the M1 has one primary display controller hardwired to eDP and one external display controller connected to a crossbar that leads to the Type C DP PHYs and the Thunderbolt packetizer. The M2 moves the primary controller to the crossbar too, so it can be repurposed to output via the Type C ports too. M3 is presumably identical. All baseline chips still only have 2 display controllers total, and this is cost driven and not easy to increase without a major die size increase since the display controllers are huge. The change to the crossbar, on the other hand, is essentially “free” and makes perfect sense to do.

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Laptops not being able to drive more than one external monitor in 2024 is straight out of clown universe.

> Laptops not being able to drive more than one external monitor in 2024 is straight out of clown universe.

Personally, I would be happy if they could drive this single external monitor flawlessly. Which is not the case, unfortunately.

It's a really bad look to confirm in this manner that Apple software-crippled the M3 MacBook Pro to drive people towards more expensive configurations.

I also don't understand the base model with 256 GB. I suspect it mosty gets purchased by fairly uninformed users on a budget, and they're going to have a terrible experience when it inevitably fills up after a bit of use and they can't upgrade the SSD anymore. It doesn't seem like the poor experience is worth the few dollars it costs Apple for the additional flash memory.

@Marcos And what about the M2 and M1 Macs that are not even getting the update? Or should we continue assuming that the wiring isn’t there?

What remains ridiculous is a user can't use two 2560x1440 Thunderbolt displays with the MacBook open - or any other non-retina displays. I feel confident in saying there is no technical or bandwidth reason that couldn't be supported with M1 chips, and yet here we are.

@Mateo Yes, that’s another question. Even assuming the internal display truly can’t be used, why is external display support tied to clamshell mode, which prevents using the internal keyboard and trackpad?

@Michael Tsai I bet they are capable of multiple displays as well but we aren't 100% sure. Can't wait for the folks working on Linux to figure it out.

>Or should we continue assuming that the wiring isn’t there?

Fingers crossed that iFixit or AnandTech or someone can one day tell us what's really going on.

My current hypothesis: the M3 changes things up slightly in that it adds a third wire, and two of them can be digitally switched. But the firmware to implement that didn't ship in time for the MBP with M3 (I wish these product names weren't so awkward).

Either way, this is better. I'm curious if the folks at work whom I got a DisplayLink-based slightly hackish solution for would be OK with instead operating the thing lid-closed.

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