Predicted display support on M2? More displays than M1? 8k? HDMI 2.1? DP Alt Mode2.0?

[theorist9]

1) As you know, the base M1 supports only 2 displays (1 external for the Air and M1 MBP, since the internal counts as one) and the M1 Pro in the MBP supports 3 (2 external plus the internal). What's the chance the M2 will support more? What would need to change for that to happen?

2) Will we see HDMI 2.1?

3) And what about 8k? That could be done with HDMI 2.1+ DSC, or with TB4 + DSC. AFAIK there are no 8k TB4 displays; there are 8k TV's, but they all use HDMI 2.1. Will 8k support have to wait until Apple produces its own 8k display? It would be nice to have the Dell 8k as an option, though even if Apple does offer 8k support, the Dell uses an older dual-cable (2 x DP 1.4, IIUC) connection that might not work with the Mac. Maybe if Apple offers 8k support, Dell will update its 8k (which, I suppose, is a business reason for Apple *not* to offer 8k support, since that could take sales from the XDR; OTOH, being able to work with higher resolution displays does provide added value; not sure what Apple's thinking on this would be).

4) Then there's DisplayPort Alt Mode 2.0. That could be very useful if Apple wants to produce a 120 Hz version of the 6k (or rumored 7k) XDR, and doesn't want to use heavy compression. According to https://en.wikipedia.org/wiki/Thunderbolt_(interface), "USB4 supports DisplayPort 2.0 over its alternative mode. DisplayPort 2.0 can support higher than 8K resolution at 60 Hz losslessly due to new UHBR 10, 13.5, and 20 signaling standards (DSC 1.2 used in DisplayPort 1.4 for that resolution is not lossless) in 8 bit and 8K 60 Hz with 10 bit color and use up to 80 Gbit/s (effective bandwidth 77.37 Gbit/s), which is double the amount available to USB data, because (just as previously in DisplayPort 1.4) it sends almost all the data in one direction (to the monitor) and can thus use all four data lanes at once.[90] Resolutions up to 16K (15360×8640) 60 Hz display with 10 bit Y'CbCr 4:4:4 or RGB are possible.[91][92]"

Even with DP Alt Mode2.0, 120 Hz on the 6k XDR would still require either DSC or chroma subsampling, but not very much. According to a calculation by John Siracusa, the uncompressed bit rate would be 78.61 Gb/s, while DP Alt Mode2.0 offers 77.37 Gb/s. Compare that with the kind of compression you'd need with HDMI 2.1 (<48 Gb/s) or TB4 in normal duplex mode (38.88 Gb/s). See: https://gist.github.com/siracusa/bb006d14e9906ac215fdee7685dc4b4c

 

[nothingtoseehere]

1) As you know, the base M1 supports only 2 displays (1 external for the Air and M1 MBP, since the internal counts as 1) and the M1 Pro in the MBP supports 3 (2 external plus the internal). What's the chance the M2 will support more? What would need to change for that to happen?

It is pure guesswork but I suspect that Apple's marketing decision is that the base "M" models only support 2 displays. So if you want to have a Macbook and two external displays, you must buy the MBP. Alas, I think that will stay but I were happy to be wrong.
In my office, the idea to switch to Apple was dead with this decision. The M1 MBA would have been perfect with the crucial exception that is does not support two external displays that we all use. For comparable Windows machines, two external monitors are supported.
"Pluginability" not the strong side of the Mac...

 

[theorist9]

It is pure guesswork but I suspect that Apple's marketing decision is that the base "M" models only support 2 displays. So if you want to have a Macbook and two external displays, you must buy the MBP. Alas, I think that will stay but I were happy to be wrong.
In my office, the idea to switch to Apple was dead with this decision. The M1 MBA would have been perfect with the crucial exception that is does not support two external displays that we all use. For comparable Windows machines, two external monitors are supported.
"Pluginability" not the strong side of the Mac...

I remember someone saying that exact thing about their office after the M1 came out. Not surprising, because the Air is perfect for routine office work, but many office workers use dual monitors to deal with spreadsheets, etc.

They could still differentiate the M1 Air and M1 Pro by having the M1 Air support 3 displays and M1 Pro support 4.

 

[thenewperson]

They could still differentiate the M1 Air and M1 Pro by having the M1 Air support 3 displays and M1 Pro support 4.

That's what I'm hoping for as well, but I'm not really holding my breath for that. 2 displays on base M1 should be the standard.

 

[theorist9]

That's what I'm hoping for as well, but I'm not really holding my breath for that. 2 displays on base M1 should be the standard.

The other thing to consider is that Apple is probably hoping the efficiency (=> battery life) and performance of the M1 will help to convert PC users. But PC laptops comparable in price to the M1's generally support at least two external displays.

Of course, they can also usually be configured with 32 GB RAM—which points up another limitation of the M1, which is being discussed on another thread.

 

[aeronatis]

They could still differentiate the M1 Air and M1 Pro by having the M1 Air support 3 displays and M1 Pro support 4.

That would actually be quite good as it would give buyers another reason to choose MacBook Pro M2 over MacBook Air M2 contrary to how it is now.

 

[leman]

I think M2 will support two external displays. Skeptical about HDMI2.1 or 8K

 

[JMacHack]

Do we know why the M1 only supports two displays? I can’t imagine it’s an artificial limitation given past MacBook support for more displays and it’s not a purely technical limitation because the M1 pro and above can support more displays.

 

[theluggage]

But PC laptops comparable in price to the M1's generally support at least two external displays.
Of course, they can also usually be configured with 32 GB RAM.

There's also the issue of making sure that there is enough GPU power (and RAM, with unified memory) to drive that number of displays smoothly - given that they are increasingly likely to be 4k or higher these days. Mac OS is quite a graphically demanding UI - especially if you need to use fractional scaling to get your preferred UI size on a 4k display. I'm not sure that I'd want to run that many displays off an 8GB M1.

Windows, at least, doesn't have the fractional scaling issue - even so, running 3 screens is a bit much for Intel integrated graphics.

The priority of the "regular" M2 will probably be - as a replacement for the regular M1 - to provide the best performance-per-watt for use in ultra-thin, fanless laptops and tablets. The fact that it's likely to be good enough for Mac Minis and iMacs too is something of a bonus. Since the M1 has been rather successful, even with its display limitations - I don't think supporting more displays will be a priority, although I wouldn't completely rule it out.

As for the RAM - you need to make sure you're comparing comparable machines not just on price (this just in: Macs aren't cheap). I'm sure there are exceptions but if you look at ultra-thin, long battery life 13" laptops with LPDDR4 RAM (such as a Dell XPS13) it's typical to find a choice of 8GB or 16GB of non-upgradeable RAM - for the same reasons as on the MacBook Air: LPDDR chips have to be surface-mount soldered and with 2 chips the max is 16GB. Less power-efficient/larger machines (like the XPS 15) with regular DDR4/5 RAM may offer 32GB and 64GB options (and may even be upgradeable). Apple, post M1, are slightly unusual in going for LPDDR RAM in everything.

It is possible, though, that the M2 will adopt a newer variant of LPDDR RAM that supports bigger individual chips - which could make 32GB RAM possible (...and it's high time that Apple started shipping 16GB as standard, certainly in the "better" models).

I'm not giving Apple a free pass on their RAM (or SSD) prices - which have always been astronomical - but with the M1 and the performance advantages of on-package LPDDR there slightly easier to swallow.

They could still differentiate the M1 Air and M1 Pro by having the M1 Air support 3 displays and M1 Pro support 4.

Trouble is, that's getting in to diminishing returns (for Apple). Three displays is more than enough for many potential Mx Pro customers. 4 isn't that great an incentive to upgrade to a Mx Pro.

Mind you, Apple could get their finger out and implement DisplayPort daisy-chaining so you could hang a couple of lower-res displays off a single DisplayPort...

 

[theorist9]

There's also the issue of making sure that there is enough GPU power (and RAM, with unified memory) to drive that number of displays smoothly - given that they are increasingly likely to be 4k or higher these days. Mac OS is quite a graphically demanding UI - especially if you need to use fractional scaling to get your preferred UI size on a 4k display. I'm not sure that I'd want to run that many displays off an 8GB M1.

Windows, at least, doesn't have the fractional scaling issue - even so, running 3 screens is a bit much for Intel integrated graphics.

I've got a 2014 MBP with an NVIDA GT750M (2 GB VRAM) that's spec'd by Apple to handle two external displays. It's currently exceeding that, driving 3 external displays, including one 4k (see the list below). I suspect that, with 8 years of advances, an M1 laptop should be able to handle two external 4k's.

As for the RAM - you need to make sure you're comparing comparable machines not just on price (this just in: Macs aren't cheap). I'm sure there are exceptions but if you look at ultra-thin, long battery life 13" laptops with LPDDR4 RAM (such as a Dell XPS13) it's typical to find a choice of 8GB or 16GB of non-upgradeable RAM - for the same reasons as on the MacBook Air: LPDDR chips have to be surface-mount soldered and with 2 chips the max is 16GB. Less power-efficient/larger machines (like the XPS 15) with regular DDR4/5 RAM may offer 32GB and 64GB options (and may even be upgradeable). Apple, post M1, are slightly unusual in going for LPDDR RAM in everything.

The comparable machine to the M1 MBP, based on cost, weight, performance, and sophistication, is the Dell XPS 13 Plus. And it uses LPPPDR5 RAM, and offers up to 32 GB.

Trouble is, that's getting in to diminishing returns (for Apple). Three displays is more than enough for many potential Mx Pro customers. 4 isn't that great an incentive to upgrade to a Mx Pro.

Mind you, Apple could get their finger out and implement DisplayPort daisy-chaining so you could hang a couple of lower-res displays off a single DisplayPort...

The problem is that 2 external displays is a very common office setup. See Post#2 by nothingtoseehere. Apple excludes themselves from this market by not allowing it on its M1 laptops.

 

[theorist9]

Do we know why the M1 only supports two displays? I can’t imagine it’s an artificial limitation given past MacBook support for more displays and it’s not a purely technical limitation because the M1 pro and above can support more displays.

I've wondered this myself. I've seen explanations offered, such as the following from Reddit, but nothing that's authoritative:

 

[leman]

Do we know why the M1 only supports two displays? I can’t imagine it’s an artificial limitation given past MacBook support for more displays and it’s not a purely technical limitation because the M1 pro and above can support more displays.

I am certain that is a hardware limitation of the display controller M1 inherited from A14. I would be very surprised if M2 couldn’t do more displays.

One also has to consider the memory bandwidth issue, on Apple Silicon the GPU renders to system RAM and the display controller reads that RAM and sends it to the video output. Since bandwidth is precious, limiting external displays ensures that the system can stay functional. But if M2 moves to LPDDR5, it will absolutely have the headroom for an additional 4K or 5K signal.

 

[guzhogi]

4) Then there's DisplayPort Alt Mode 2.0. That could be very useful if Apple wants to produce a 120 Hz version of the 6k (or rumored 7k) XDR, and doesn't want to use heavy compression. According to https://en.wikipedia.org/wiki/Thunderbolt_(interface), "USB4 supports DisplayPort 2.0 over its alternative mode. DisplayPort 2.0 can support higher than 8K resolution at 60 Hz losslessly due to new UHBR 10, 13.5, and 20 signaling standards (DSC 1.2 used in DisplayPort 1.4 for that resolution is not lossless) in 8 bit and 8K 60 Hz with 10 bit color and use up to 80 Gbit/s (effective bandwidth 77.37 Gbit/s), which is double the amount available to USB data, because (just as previously in DisplayPort 1.4) it sends almost all the data in one direction (to the monitor) and can thus use all four data lanes at once.[90] Resolutions up to 16K (15360×8640) 60 Hz display with 10 bit Y'CbCr 4:4:4 or RGB are possible.[91][92]"

As this says, DisplayPort 2.0 bandwidth uses double the bandwidth of USB4 and Thunderbolt 3 / 4, and both interfaces are out of Apple's control. So until USB/TB 5+ comes out that meets or exceeds DisplayPort 2 speeds, we probably won't see uncompressed, high frame rate and/or HDR 4K+ any time soon.

I've wondered this myself. I've seen explanations offered, such as the following from Reddit, but nothing that's authoritative:

View attachment 2003351

If true, kinda wish Apple removed this limitation when first design the M1. Heck get rid of the limitation entirely. I'm not one, but I'm sure there are a few people would like to use an iPad with multiple external displays. Especially since higher end iPads now have the same SoC as Macs.

 

[JMacHack]

I am certain that is a hardware limitation of the display controller M1 inherited from A14. I would be very surprised if M2 couldn’t do more displays.

One also has to consider the memory bandwidth issue, on Apple Silicon the GPU renders to system RAM and the display controller reads that RAM and sends it to the video output. Since bandwidth is precious, limiting external displays ensures that the system can stay functional. But if M2 moves to LPDDR5, it will absolutely have the headroom for an additional 4K or 5K signal.

I've wondered this myself. I've seen explanations offered, such as the following from Reddit, but nothing that's authoritative:

View attachment 2003351

If both these are true then I could see the M2 supporting more displays. That is, if it’s a completely new design.

 

[Tagbert]

I am certain that is a hardware limitation of the display controller M1 inherited from A14. I would be very surprised if M2 couldn’t do more displays.

One also has to consider the memory bandwidth issue, on Apple Silicon the GPU renders to system RAM and the display controller reads that RAM and sends it to the video output. Since bandwidth is precious, limiting external displays ensures that the system can stay functional. But if M2 moves to LPDDR5, it will absolutely have the headroom for an additional 4K or 5K signal.

But the M1 Pro/Max/Ultra also inherit the same basic display controller. They just add more execution units.

 

[jdb8167]

If Apple wants to claim Thunderbolt 4 compatibility with the M2 then they will have to support 2 4K or 1 8K display per thunderbolt 4 controller. The reason that Apple only claims Thunderbolt/USB4 compatibility for the M1 is that they don't meet the minimum TB 4 display connectivity requirements.

Double the minimum video and data requirements of Thunderbolt 3.

• Video: Support for two 4K displays or one 8K display.

From https://newsroom.intel.com/news/introducing-thunderbolt-4-universal-cable-connectivity-everyone/

 

[jdb8167]

But the M1 Pro/Max/Ultra also inherit the same basic display controller. They just add more execution units.

That isn't likely to be true. There is no reason Apple couldn't have beefed up the display controllers on the Pro/Mac/Ultra to make them true Thunderbolt 4 ports.

 

[Tagbert]

That isn't likely to be true. There is no reason Apple couldn't have beefed up the display controllers on the Pro/Mac/Ultra to make them true Thunderbolt 4 ports.

That just means that the M1 display performance is not an inherent limitation of the display controller but in how it is configured for the M1 specifically.

 

[jdb8167]

That just means that the M1 display performance is not an inherent limitation of the display controller but in how it is configured for the M1 specifically.

Maybe, but the only reason I can think that Apple would do that is for battery life. And I don't see how you get more battery life if the extra display controller isn't used. Why are you so sure that they use the same controller?

 

[Tagbert]

Maybe, but the only reason I can think that Apple would do that is for battery life. And I don't see how you get more battery life if the extra display controller isn't used. Why are you so sure that they use the same controller?

Apple has shown with Apple Silicon that their strategy is to create a basic CPU and GPU core and then create low end and pro version that include more or less of the same basic unit. I don’t mean that there are not differences in how the display controllers are setup on the M1 vs the Pro but that it is not inherent in the GPU cores shared with the A14. It’s more along the lines of how the overall package is configured to support the i/o channels.

 

[jdb8167]

Apple has shown with Apple Silicon that their strategy is to create a basic CPU and GPU core and then create low end and pro version that include more or less of the same basic unit. I don’t mean that there are not differences in how the display controllers are setup on the M1 vs the Pro but that it is not inherent in the GPU cores shared with the A14. It’s more along the lines of how the overall package is configured to support the i/o channels.

Obviously this isn't true for all components though. The ProRes hardware is unique to the Pro/Max line for example.

 

[darngooddesign]

1) As you know, the base M1 supports only 2 displays (1 external for the Air and M1 MBP, since the internal counts as one) and the M1 Pro in the MBP supports 3 (2 external plus the internal). What's the chance the M2 will support more? What would need to change for that to happen?

Maybe on the M3, but I doubt it on the M2.

You would have to change the way Apple wants to differentiate the computers.

 

[darngooddesign]

...I'm not one, but I'm sure there are a few people would like to use an iPad with multiple external displays. Especially since higher end iPads now have the same SoC as Macs.

That's a different discussion, but iPadOS only mirrors on an external display so connecting two displays wouldn't do anything useful. The iPad would need to have real external display support first.

 

[ArrayDecay]

I want my...I want my...I want my M2 Mac.

 

[theorist9]

I am certain that is a hardware limitation of the display controller M1 inherited from A14. I would be very surprised if M2 couldn’t do more displays.

One also has to consider the memory bandwidth issue, on Apple Silicon the GPU renders to system RAM and the display controller reads that RAM and sends it to the video output. Since bandwidth is precious, limiting external displays ensures that the system can stay functional. But if M2 moves to LPDDR5, it will absolutely have the headroom for an additional 4K or 5K signal.

Do we know about what fraction of the M1's bandwidth dual 4k displays would actually require? The 8 y.o. GT750M on my 2014 MBP is spec'd to drive 2 external displays, and is currently driving 3 (including one 4k). There may be a response hit with 3 displays (hard to tell for certain), but with just two (4k + WUXGA), there's definitely not.