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mattsea

macrumors newbie
Original poster
Mar 7, 2021
3
1
I have an M1 MBP. I connect it to my external display (DELL S2721QS) using a HyperDrive Viper hub.


When my MBP is in clamshell mode, the external display works at 4K 60Hz resolution. When the MBP is open, the external display only works at 4K 30Hz.

My hub and HDMI cable are both capable of 4K 60Hz, as shown by the fact that it works when in clamshell mode. I have tried a second HDMI cable and encounter the same issue. Does anyone have experience with driving a 4K 60Hz display with their M1 MBP open? Is this possible?
 

mattsea

macrumors newbie
Original poster
Mar 7, 2021
3
1
I've figured out the issue, thanks to help from another site. Leaving details here in case it helps anyone else.

The technical specs say the M1 MBP "simultaneously supports full native resolution on the built-in display in millions of colours and one external display with up to 6K resolution at 60Hz".

It does not appear to simultaneously support 4K at 60Hz on an external display AND a scaled resolution on the built-in display. I was using the built-in display at a scaled resolution - 1680 x 1050 - rather than the default - 1440 x 900. When using the default resolution for the internal display, I can have 4K60Hz on the external display with the laptop open.
 
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