New Apple Silicon M4 and M5 HiDPI Limitation on 4K External Displays
by smcleod on 3/30/2026, 1:43:20 AM
https://smcleod.net/2026/03/new-apple-silicon-m4-m5-hidpi-limitation-on-4k-external-displays/
Comments
by: nuker
Send it to Tim Cook email. It worked for me fixing DisplayPort DSC bug. After Catalina, later MacOSes lost ability to drive monitors at higher than 60Hz refresh.<p>Apple support tortured me with all kinds of diagnostics, with WontFix few weeks later. Wrote email and it got fixed in Sonoma :)<p><a href="https://egpu.io/forums/mac-setup/4k144hz-no-longer-available-after-upgrade-to-big-sur/paged/10/" rel="nofollow">https://egpu.io/forums/mac-setup/4k144hz-no-longer-available...</a>
3/30/2026, 3:07:02 AM
by: wronglebowski
Props to the author for putting in what looks like ton of work trying to navigate this issue, shame they have to go to these lengths to even have their case considered.
3/30/2026, 2:42:26 AM
by: skullone
I thought I was going crazy when my new m4 seemed "fuzzier" on my external 4ks. I tried replicating settings from my old MacBook to no avail. I wonder if Apple is doing this on purpose except for their own displays.
3/30/2026, 2:55:09 AM
by: arjie
I'm sure you've already given this a crack via some other technique (I just Cmd-F for it and didn't find) but I have had monitors with confusing EDIDs before that MacOS didn't handle well and the "screenresolution" CLI app <a href="https://github.com/jhford/screenresolution" rel="nofollow">https://github.com/jhford/screenresolution</a> always let me set an arbitrary one. It was the only way to get some monitors to display at 100 Hz for me and worked very well for that since the resolution is mostly sticky.
3/30/2026, 3:23:47 AM
by: LuxBennu
Sadly I have the issue on a new m5 air. I have a 60hz 4k work monitor and two high refresh 4k gaming displays. The 60hz pairs fine with either gaming monitor, but the two gaming ones together and one just doesn't get recognized. Spent way too long trying new cables before realizing it's a bandwidth limitation.
3/30/2026, 3:29:41 AM
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3/30/2026, 6:23:16 AM
by: wmf
This is not a normal retina configuration. This is a highly unusual configuration where the framebuffer is much larger than the screen resolution and gets scaled down. Obviously it sucks if it used to work and now it doesn't but almost no one wants this which probably explains why Apple doesn't care.
3/30/2026, 3:03:02 AM
by: tgma
This might be a dumb question: Is the author looking to run 4k display at HiDPI 8k framebuffer and then downscale? What's the advantage of doing so versus direct 4k low-DPI? Some sort of "free" antialiasing?
3/30/2026, 5:10:14 AM
by: Someone
> This aligns with our findings. The M4/M5 DCP firmware implements a conservative framebuffer pre-allocation strategy that:<p>> Caps the HiDPI backing store to approximately 1.75x the native resolution (6720x3780 for 3840x2160 native), rather than the 2.0x needed for full HiDPI (7680x4320)<p>So, that could be an off by one bug? That might be testable by tweaking the system to think the display supports an even higher resolution.<p>Also, instead of messing with the Display Override Plist, patching drivers, etc, did they try using the “Advanced…” button in the “Displays” UI? They don’t mention they did.<p>For me (with a 27 inch 4K monitor not on M4 or M5) that replaces the 5-way choice by one with a list of 11 choices. With the then appearing “Show all resolutions” toggle, that becomes 18.
3/30/2026, 5:44:20 AM
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3/30/2026, 5:40:57 AM
by: mil22
This would be even more compelling if you included screenshots with magnified detail insets showing the text blur.
3/30/2026, 3:19:02 AM
by: bsimpson
Wouldn't HiDPI be 1080p@2x? Is that still available?
3/30/2026, 3:00:38 AM
by: pier25
I use a 4K 32'' Asus ProArt monitor and didn't notice any difference between my M2 Pro and my M4 Pro (on Sequoia). I will admit my eyesight is not the best anymore but I think I would notice given I'm a bit allergic to blurry monitors.<p>Anyway I will run the diagnostic commands and see what I get.
3/30/2026, 3:49:22 AM
by: compounding_it
The ideal work/coding resolutions and sizes for macOS that I would suggest if you are going down this rabbit hole.<p>24 inch 1080p 24 inch 4k (2x scaling) 27 inch 1440p 27 inch 5k (2x scaling) 32 inch 6k (2x scaling)<p>Other sizes are going to either look bizarre or you’ll have to deal with fractional scaling.<p>Given that 4k is common in 27/32 inches and those are cheap displays these kinds of problems are expected. I have personally refused to accept in the past that 27 inch 4k isn’t as bad as people say and got one myself only to regret buying it. Get the correct size and scaling and your life will be peaceful.<p>I would recommend the same for Linux and Windows too tbh but people who game might be fine with other sizes and resolutions.
3/30/2026, 3:54:11 AM
by: keyle
This is the sort of Apple gotchas that really upset me.<p>They've got a good thing going, but they keep finding ways to alienate people.
3/30/2026, 3:36:58 AM
by: whatever1
How did none of the Apple devs notice this? 4k 32" inch is the industry standard for HiDPI monitors.
3/30/2026, 3:13:21 AM
by: tmsh
You might need a higher quality usb cable. I run ok with LG 5k display and MacBook Pro m4 max.
3/30/2026, 5:46:26 AM
by: pier25
Is this for specific verisons of macOS?<p>The article doesn't mention it.
3/30/2026, 3:22:34 AM
by: jval43
Not <i>again</i>! Had these issues with 2016 Macbook Pro (the touchbar one).<p>That one also wasn't a hardware limitation as it ran my displays just fine in bootcamp, but macOS would just produce fuzzy output all the way.<p>It's infuriating.
3/30/2026, 5:03:26 AM
by: spoaceman7777
Yep. Apple sells 5k displays, which work fine.<p>Just another case of Apple intentionally going against established open standards to price gouge their users.<p>I wouldn't mind it as much if I didn't have to hear said users constantly moaning in ecstasy about just how much better "Apple's way" is.<p>High quality desktop Linux has been made real by KDE, and the AI-fueled FOSS development boom is accelerating this eclipse of proprietary nonsense like this.<p>If you're a developer, you should be using a system that isn't maintained by a company that intentionally stabs developers in the back at every turn. (Unless you're into that. U do u.)
3/30/2026, 4:48:57 AM
by: lovegrenoble
They do this on purpose ...
3/30/2026, 4:18:24 AM
by: chaostheory
What are they doing with MacOS? Is this due to VisionOS?
3/30/2026, 4:51:18 AM
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3/30/2026, 3:11:46 AM
by: jiveturkey
TFA doesn't say -- does anyone know if this applies to 5k and 6k monitors? On my 5k display on a M4 Max, I see the default resolution in system settings is 2560x1440. Which is what I'd expect.<p>If the theory about framebuffer pre-allocation strategy is to hold any water, I would think that 5k and 6k devices would suffer too, maybe even more. Given that you can attach 2x 5k monitors, the pre-allocation strategy as described would need to account for that.
3/30/2026, 4:13:03 AM
by: PedroBatista
Now I know I was not crazy and the "cheap" 4K screen I bought a couple months ago doesn't actually suck.<p>Tim Apple's Apple has been fu#$%& me again..
3/30/2026, 3:07:29 AM
by: comex
Well, it sounds like a real issue, but the diagnosis is AI slop. You can see, for example, how it takes the paragraph quoted from waydabber (attributing the issue to dynamic resource allocation) and expands it into a whole section without really understanding it. The section is in fact self-contradictory: it first claims that the DCP firmware implements framebuffer allocation, then almost immediately goes on to say it's actually the GPU driver and "the DCP itself is not the bottleneck". Similar confusion throughout the rest of the post.
3/30/2026, 3:11:24 AM
by: imrozim
[dead]
3/30/2026, 4:55:38 AM
by: 7e
[flagged]
3/30/2026, 3:54:18 AM