PS. I have no horse in this race. I have an M1 Pro and still only use one external monitor as a professional software developer. I wonder how many M1/M2 owners actually want two external monitors support? Would M1/M2 owners sacrifice CPU or GPU performance for two external monitor support?
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Asahi Creator: 1 monitor support is because of hardware limitation
- Thread starter senttoschool
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PS. I have no horse in this race. I have an M1 Pro and still only use one external monitor as a professional software developer. I wonder how many M1/M2 owners actually want two external monitors support? Would M1/M2 owners sacrifice CPU or GPU performance for two external monitor support?
They must have determined for the machines that the M2 is fitted in, the majority of users will not need more than 1 external displays as a matter of marketing research. Not saying I wouldn't welcome them supporting more, but if it is a silicon design choice as noted by Hector, then it is clear this is the case.
Apple created the chip and the hardware, they could have done something in the design stage. The reason for only 1 monitor support is because Apple designed it that way. They are not dependant on anyone else's hardware and can't say because of this gpu or that cpu we are limited. They made it all and I am sure they knew about the limitation early on and decided the market was not big enough for multi monitor support to warrant whatever costly changes would have been necessary.
One thing to keep in mind is that the same M1/M2 goes into the iPad Pro, iPad Air, and iMac. There is no reason to waste precious transistors on supporting two displays on those devices.
It does support two displays though. The other one is just usually built-in unlike in the Mac mini.
If you look at the finished design of cause it is a "hardware limitation" because Apple made the design choice to not support more than 1 external monitor.
It would reduce performance or increase cost for extra monitors, but how much the machine is priced is also decided by Apple(and they chose to price an 8GB RAM with 256GB SSD laptop at $1200 in 2022).
Apple can have their complex reasons behind each design choice, but we as the customers can also complain about the design choice that increase our cost/limit our use cases. Yes, I know I can pay more and get the Pro/Max chip for extra monitors, but it is not cheap especially when the additional performance is not meaningful for my use case.
Disclaimer: I purchased M1 Max just for 2 more external monitors over the M1 Pro, I am willing to pay if they can provide the feature I want, but I still paid for the extra GPU cores which I don't need.
It would reduce performance or increase cost for extra monitors, but how much the machine is priced is also decided by Apple(and they chose to price an 8GB RAM with 256GB SSD laptop at $1200 in 2022).
Apple can have their complex reasons behind each design choice, but we as the customers can also complain about the design choice that increase our cost/limit our use cases. Yes, I know I can pay more and get the Pro/Max chip for extra monitors, but it is not cheap especially when the additional performance is not meaningful for my use case.
Disclaimer: I purchased M1 Max just for 2 more external monitors over the M1 Pro, I am willing to pay if they can provide the feature I want, but I still paid for the extra GPU cores which I don't need.
I think it's all been calculated. They probably have the data on how many users actually use external monitor and for how many. And they made the decision to only allow 1 on the base M Apple silicon to put more die space for other things. And it's not like there's no solution, the M1 Pro/Max/Ultra exist to serve those needs. And there are workarounds like using display link.
The Macbook Air is fine. BUT, this only makes more case for the 13" Macbook Pro to not exist. It carriers the Pro brand, but has all the limitations of the Macbook Air. It literally carries the Pro brand only because it has a fan...
The Macbook Air is fine. BUT, this only makes more case for the 13" Macbook Pro to not exist. It carriers the Pro brand, but has all the limitations of the Macbook Air. It literally carries the Pro brand only because it has a fan...
It's not just space and cost - more transistors use more battery power and generate more heat, in a chip designed for fanless tablets and ultraportables.
...there's a deeper technical question, though, as to why a machine that can support a 6K display couldn't have been designed to support two 4K displays (each needing less than half the bandwidth) - which was the situation with the outgoing Intel iMac. Or why they can't support MST (DisplayPort daisy-chaining) on Macs. I'll leave that for someone with the technical chops, but the answer probably comes down to "more transistors/power/heat/space & supporting non-Apple displays isn't Apple's priority". As @wonderings said, the chip is Apple's design and they could have chosen to support more displays back when it was on the drawing board.
Ultimately, you just have to trust Apple's market research - I can easily believe that the majority of MacBook Airs sold are never used with an external display (excluding AirPlay), that the average number of displays connected is somewhere between 0 and 1, and that many customers who want 2 or mode displays also want the extra power and connectivity of a M1 Pro.
I think the real problem is that the 13" MBP, the higher-end 24" iMac and the missing higher-end Mac Mini/Low-end Studio should be using M1 Pro SoCs, not the same chip as the iPad! The fact that the M1/M2 has the raw power to handle some quite substantial audio/video/graphics workflows has attracted users who wouldn't have looked twice at an entry-level Intel with the ultra-low-powered Intel offerings. Even the old low-end 13" MBP used to have a higher-power-rated Intel processor than the Air. What the people wanting two ext. displays on a M1/M2 machine probably need is a 13" MBP with a M1 Pro and basic display, rather than paying for a fancy 14" HDR display in a laptop that is going to spend most if it's time in clamshell mode on a desk.
This.
People seem to forget that M2 is near entry level.
Yes it is a beast in terms of performance vs. the rest of the market, but its intended to be (within the context of the apple lineup) an entry level casual user machine.
Intended for use mainly by itself away from a desk. I'd suggest most MBA users use ZERO external displays 99% of the time, and those who do use one (rarely) are when they plug into a single projector to do a presentation. Hence, it doesn't even have a HDMI port.
The work-around for multiple displays not being an option is to just get one single display that is big enough.
🤷♂️
Seeing this, I have a weird theory about this now... To go in tandem with this information about display controllers:
The tweets say there is an internal display controller "(plus the internal one which is on top of the ECPUs, not annotated above)."
I think the external display units rely on having 4 GPU cores to reliably drive one 6K 60Hz monitor (i.e.: one pro display XDR, which is apple's benchmark) and 3 minimum for the internal display controller or HDMI 2.0 interface. On machines that don't have a display built in, the hdmi 2.0 port gets tied to the internal display unit.
So M1: 1 ext disp controller and 1 internal controller & 7/8 GPU cores:
4 to external display and 3/4 for the internal/hdmi 2.0 display out.
M1 Pro: 2 external display controllers and 1 internal controller & 14/16 GPU cores.
8 to external displays. 4 to internal (Since the MBP has a 2.5k 120Hx display it needs 4 can't do 3) that leaves 2/4 depending on GPU config for another external display where the 4 aren't guaranteed based on config bought so apple didn't even bother putting the third ext display silicon in there.
M1 Max: 24 GPU cores is the minimum config for this chip so here we have 4 external display controllers and 1 internal.
4 x 5 = 20 cores. (technically the hdmi interface is limited to 4x60Hz because HDMI 2.0 port)
This also utilizes all the ports on the macbook pro which has 3 TB4 ports and 1 HDMI 2.0 which is why they didn't bother putting in another external display controller.
M1 Ultra: Here since we're on desktop the internal display unit is just beign assigned to the hdmi 2.0 port on the back of the mac studio. But not sure what's goin on here tbh but perhaps the display output silicon is just disabled on the "Second" m1 max chip on the M1 Ultra. Perhaps Apple thinks that customers don't need more than 5 external displays, which is reasonable quite frankly. But also there are only 4 TB4 ports and 1 HDMI port on the back of the mac studio so it's not like you can plug more monitors in directly anyways.
Thank you for coming to my TED Talk 😂
Edit: Spelling
The tweets say there is an internal display controller "(plus the internal one which is on top of the ECPUs, not annotated above)."
I think the external display units rely on having 4 GPU cores to reliably drive one 6K 60Hz monitor (i.e.: one pro display XDR, which is apple's benchmark) and 3 minimum for the internal display controller or HDMI 2.0 interface. On machines that don't have a display built in, the hdmi 2.0 port gets tied to the internal display unit.
So M1: 1 ext disp controller and 1 internal controller & 7/8 GPU cores:
4 to external display and 3/4 for the internal/hdmi 2.0 display out.
M1 Pro: 2 external display controllers and 1 internal controller & 14/16 GPU cores.
8 to external displays. 4 to internal (Since the MBP has a 2.5k 120Hx display it needs 4 can't do 3) that leaves 2/4 depending on GPU config for another external display where the 4 aren't guaranteed based on config bought so apple didn't even bother putting the third ext display silicon in there.
M1 Max: 24 GPU cores is the minimum config for this chip so here we have 4 external display controllers and 1 internal.
4 x 5 = 20 cores. (technically the hdmi interface is limited to 4x60Hz because HDMI 2.0 port)
This also utilizes all the ports on the macbook pro which has 3 TB4 ports and 1 HDMI 2.0 which is why they didn't bother putting in another external display controller.
M1 Ultra: Here since we're on desktop the internal display unit is just beign assigned to the hdmi 2.0 port on the back of the mac studio. But not sure what's goin on here tbh but perhaps the display output silicon is just disabled on the "Second" m1 max chip on the M1 Ultra. Perhaps Apple thinks that customers don't need more than 5 external displays, which is reasonable quite frankly. But also there are only 4 TB4 ports and 1 HDMI port on the back of the mac studio so it's not like you can plug more monitors in directly anyways.
Thank you for coming to my TED Talk 😂
Edit: Spelling
I think Hector Martin is spot on with this:
Basically, he speculates that Apple focuses on power efficiency above all, so they include large SDRAM buffers in their display controllers, so they can put the main RAM into energy saving mode while doing scan out. That will definitely help them in achieve impressive battery life while driving a high-res display. And since SDRAM takes a lot of die space, they can only integrate this many controllers.
Basically, he speculates that Apple focuses on power efficiency above all, so they include large SDRAM buffers in their display controllers, so they can put the main RAM into energy saving mode while doing scan out. That will definitely help them in achieve impressive battery life while driving a high-res display. And since SDRAM takes a lot of die space, they can only integrate this many controllers.
I'd say he's spot on.
run powermetrics on an apple silicon macbook pro some time. Total package power (CPU+GPU) when i did this today with my regular workload open (but mostly idle apart from teams) in the background was 0.65 watts.
2/3 of a watt! For BOTH CPU AND GPU in total!
The power consumption on this machine (14" pro) is insane. In a good way!
SRAM buffers would certainly help!
Don't forget that the package power includes DRAM power as well
And that's not just any old RAM, but 256-bit high-bandwidth 8-channel RAM.I think he's missing something.
M1/M2 are limited in regards to number of displays but not in regards to number of DisplayPort connections.
M1 and M2 can support 2 displays with 3 DisplayPort connections:
1: one internal (or HDMI for M1 Mac mini) (one DisplayPort connection)
2: one Thunderbolt (up to two DisplayPort connections)
3 DislayPort connections is as good as an Intel GPU.
M1 Pro supports 3 displays with 5 DisplayPort connections:
1: one internal (one DisplayPort connection)
2a: one HDMI and one Thunderbolt (up to 3 DisplayPort connections)
2b: two Thunderbolt (up to 4 DisplayPort connections)
M1 Max supports 5 displays with up to 8 DisplayPort connections:
1: one internal (one DisplayPort connection)
2a: one HDMI and 3 Thunderbolt (up to 7 DisplayPort connections)
2b: 4 Thunderbolt (up to 6 DisplayPort connections) There's only 3 Thunderbolt ports so one of them needs to connect two displays using a Thunderbolt hub/dock/adapter. Since there are enough DisplayPort connections, I don't see any reason why 4 Apple Pro Display XDR displays couldn't be connected since they use only HBR2 linkrate with DSC (you can tell they are not using dual HBR3 mode by checking the USB speed).
5 displays beats Nvidia GPUs. It also beats most AMD GPUs. What GPU do you know has 8 DisplayPort connections?
The extra DisplayPort connections cannot be used for additional displays. They can only be used for dual link SST displays which take two DisplayPort connections, one for each half of the display. For example, you can connect a Dell UP2715K to an M1 Mac using two DisplayPort cables and the M1 Mac will output 5120x2880 by sending 2560x2880 to each half of the display. The same thing is true for an LG UltraFine 5K which takes two DisplayPort connections over Thunderbolt - one for each half of the display. Each half is a tile. These displays are dual tile displays.
If he's making Linux graphics drivers for M1 Macs, then maybe he can utilize the extra DisplayPort connections by making pairs of displays behave like a dual tile display.
M1/M2 are limited in regards to number of displays but not in regards to number of DisplayPort connections.
M1 and M2 can support 2 displays with 3 DisplayPort connections:
1: one internal (or HDMI for M1 Mac mini) (one DisplayPort connection)
2: one Thunderbolt (up to two DisplayPort connections)
3 DislayPort connections is as good as an Intel GPU.
M1 Pro supports 3 displays with 5 DisplayPort connections:
1: one internal (one DisplayPort connection)
2a: one HDMI and one Thunderbolt (up to 3 DisplayPort connections)
2b: two Thunderbolt (up to 4 DisplayPort connections)
M1 Max supports 5 displays with up to 8 DisplayPort connections:
1: one internal (one DisplayPort connection)
2a: one HDMI and 3 Thunderbolt (up to 7 DisplayPort connections)
2b: 4 Thunderbolt (up to 6 DisplayPort connections) There's only 3 Thunderbolt ports so one of them needs to connect two displays using a Thunderbolt hub/dock/adapter. Since there are enough DisplayPort connections, I don't see any reason why 4 Apple Pro Display XDR displays couldn't be connected since they use only HBR2 linkrate with DSC (you can tell they are not using dual HBR3 mode by checking the USB speed).
5 displays beats Nvidia GPUs. It also beats most AMD GPUs. What GPU do you know has 8 DisplayPort connections?
The extra DisplayPort connections cannot be used for additional displays. They can only be used for dual link SST displays which take two DisplayPort connections, one for each half of the display. For example, you can connect a Dell UP2715K to an M1 Mac using two DisplayPort cables and the M1 Mac will output 5120x2880 by sending 2560x2880 to each half of the display. The same thing is true for an LG UltraFine 5K which takes two DisplayPort connections over Thunderbolt - one for each half of the display. Each half is a tile. These displays are dual tile displays.
If he's making Linux graphics drivers for M1 Macs, then maybe he can utilize the extra DisplayPort connections by making pairs of displays behave like a dual tile display.
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Aren't these two different things? Number of total displays depends on how many independent signals the display controllers can output. and number of display port connections depends on how these signals can be packaged and transported across the PCIe bus. I don't see why a display controller shouldn't be able to utilise multiple DP connections to stream out the signal.
But is battery life important when the display can deliver power through the same cable?
Yeah that's a good point. It is certainly critically important for the internal display, not so much when you have external display connected, as you should have handle access to power anyway. Maybe for future Apple Silicon generations they can implement two kinds of display controllers — a "big" one for the interns display with focus on power efficiency and some "small" ones for external displays. Who knows.
That's what the tweet is saying, yes.
What they did not do is limit the chip arbitrarily.
The only time I’ll be hooking up my M2 MBA to an external screen is for giving presentations, so one external display is plenty. I’m sure that I’m very much in the majority on this.
When I was a software engineer, yes, I used multiple monitors. Did I need them? Not really, but it was nice.
The #1 use case for this machine is portability and general use (for me, that means research, writing, lightweight stats work, etc), and for that all reviews seem to agree that it absolutely shines.
This “limitation” is yet another non-issue. If the machine doesn’t meet your needs, don’t buy one. This is just getting absurd.
When I was a software engineer, yes, I used multiple monitors. Did I need them? Not really, but it was nice.
The #1 use case for this machine is portability and general use (for me, that means research, writing, lightweight stats work, etc), and for that all reviews seem to agree that it absolutely shines.
This “limitation” is yet another non-issue. If the machine doesn’t meet your needs, don’t buy one. This is just getting absurd.
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Using your example, to do any type of research and writing efficiently, is putting up browser in one monitor and document/slidedeck in another too much to ask here? Two 1080p monitors can be had for under $100 and are common setup for a lot of school teachers and students, this is not a "pro" feature at all for the average users.
Technical question:
I understand the chip only having 1 display controller. And I understand the limitations of 1 Thunderbolt bus.
My only question has been, can it run 2 daisy chained 4K displays? Because that should work over 1 bus.
I haven’t seen any info about this.
I understand the chip only having 1 display controller. And I understand the limitations of 1 Thunderbolt bus.
My only question has been, can it run 2 daisy chained 4K displays? Because that should work over 1 bus.
I haven’t seen any info about this.
Sorry, but no thanks. I spend only maybe 20% of my computer time at my desk. I spend time in classes, collaborating with others in their offices or the library, in conference rooms or other collaboration spaces, with patients & clients, etc etc. A workflow that only works 20% of the time is worthless to me.
Much easier and better to have a functional workflow that I can use anywhere. And I have that with software that has no need for multiple monitors. I use the browser to find articles and sources, pull them into my scrivener project where I can read them, take notes, and write in a combination of side-by-side panes and tabs. And if I need to build a slide deck, that’s what Command-Tab is for. And I can do all that wherever I am.
Really, even when I was developing software, I never really needed more than one other monitor (external monitor for Xcode/editor, device screen for testing of Mac/web apps. Was it nice to have two full monitors? Sure. But then I didn’t really do that kind of work except at my desk.
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As an example of what we're talking about: people have connected three LG UltraFine 5K displays and a HDMI display to a M1 Max. That's 8 DisplayPort signals. The DisplayPort ports can be seen in the ioreg separated from the displays.
But the two tiles (each a DisplayPort signal) of a dual tile display are mostly independent. Why can't they behave totally independently? As far as I know, each tile uses the same DisplayPort SST signal as a normal single tile display. Maybe there's some timing issue where they need to have the same resolution/timing and need to be in sync.
Now, if you take two displays and modify their EDID so they report themselves as two halves of a single display then they could probably work in macOS as a single display. Two independent displays won't care about having the same timing or being in sync with the other display as long they accept the timing.
You could maybe do the same in Linux, but add another layer so the two halves appear as separate displays again.
A Thunderbolt port of an M1/M2 Mac can output two DisplayPort signals but the second DisplayPort signal can only be used by a dual tiled display such as the LG UltraFine 5K or the Dell UP2715K or the LG 5K2K display.
The Dell UP3218K is also a dual tile display but I don't think Apple allows 8K for Apple Silicon. Apple added support for 8K60 for the Dell UP3218K in macOS Ventura but only for Mac Pro 2019 (unless you use a patch for other Intel Macs).
M1/M2 Mac don't support 2 daisy changed 4K Thunderbolt displays because it can only support one display from Thunderbolt. You need M1 Pro or M1 Max for more displays, or use DisplayLink.
macOS doesn't support MST for multiple displays but does support MST for old 4K60 dual tile displays that used a stream for each 1920x2160 half of the display. Apple Silicon Macs don't support those old 4K60 dual tile displays.
macOS supports other features of MST though:
- convert fast and narrow DisplayPort to slow and wide DisplayPort. For example, the. CalDigit SOHO can convert HBR3 x2 with DSC to HBR2 x4 with or without DSC decompression. Except the CalDigit SOHO can't do 10bpc with DSC (which makes it unable to do 4K60 10bpc RGB) and macOS usually disables DSC except for Catalina where it was enabled by default or except for Apple's displays that support DSC (Apple Studio Display and Apple Pro Display XDR). Apple has a USB-C to HDMI 2.0 dongle that also can support HBR3 x2 with DSC to HBR2 x4 with HDMI 2.0 conversion but I think DSC is not enabled by default after Catalina.
- MST can mirror a DisplayPort signal to multiple displays.