Question Showing 120hz but monitor is 240hz

Sep 18, 2020
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I just purchased a monitor with 240hz refresh rate. I'm not a gamer and am trying it out to see if it helps with migraines from too much screen time. I'm not particularly tech savvy. I just set it up, but it says it's at 120hz. When I go to Display Preferences on my MacBook, the refresh rate options are 50, 60, and 120 hz.
  • Monitor: Alienware - 24.5" IPS LED FHD FreeSync and G-SYNC Compatible Monitor - model # AW2521HFL
  • Laptop: Macbook Air, MacOs Catalina, 2017
  • Connected via HDMI cable (came with the monitor) to Insignia Mini Display Port to HDMI Adapter for Mac (4k ultra HD, just purchased)
 

Darkbreeze

Retired Mod
HDMI doesn't support 240hz at 4k unless you have an HDMI 2.1 capable graphics card AND are using DSC (Display stream compression). Otherwise it only supports 144hz, for HDMI 2.1, or 60Hz for HDMI 2.0-2.0b. HDMI 1.4b supports just 30hz at 4k over HDMI. The fact that you are actually using a displayport output is probably the only reason you are actually able to achieve 120hz. Displayport 1.4-1.4a can do 4k at 120hz. You need displayport 2.0 to do anything higher, such as 240hz.

https://www.tomshardware.com/features/displayport-vs-hdmi-better-for-gaming
 
Sep 18, 2020
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HDMI doesn't support 240hz at 4k unless you have an HDMI 2.1 capable graphics card AND are using DSC (Display stream compression). Otherwise it only supports 144hz, for HDMI 2.1, or 60Hz for HDMI 2.0-2.0b. HDMI 1.4b supports just 30hz at 4k over HDMI. The fact that you are actually using a displayport output is probably the only reason you are actually able to achieve 120hz. Displayport 1.4-1.4a can do 4k at 120hz. You need displayport 2.0 to do anything higher, such as 240hz.

https://www.tomshardware.com/features/displayport-vs-hdmi-better-for-gaming
Thank you! Is it possible for me to get to 240hz with my 2017 Macbook Air? Or is that not possible?
 
HDMI doesn't support 240hz at 4k unless you have an HDMI 2.1 capable graphics card AND are using DSC (Display stream compression).
It's a 1080p monitor.
  • Monitor: Alienware - 24.5" IPS LED FHD FreeSync and G-SYNC Compatible Monitor - model # AW2521HFL
  • Connected via HDMI cable (came with the monitor) to Insignia Mini Display Port to HDMI Adapter for Mac (4k ultra HD, just purchased)
It is a limitation of your adapter. Please refer to Section 5.5 of the pinned thread, you need specific types of adapters to get more than 1080p 120 Hz.
 

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