At what resolution does High-resolution HDMI operate at 120 Hz?

High-resolution HDMI can operate at 120 Hz with a 4K resolution. This capability is largely due to the HDMI 2.1 specification, which supports higher resolutions and refresh rates. For 4K resolution, which is 3840 x 2160 pixels, HDMI 2.1 allows for refresh rates up to 120 Hz, enabling a smoother and more responsive viewing experience, particularly beneficial for gaming and high-frame-rate content.

In contrast, resolutions like 720p and 1080p do not require such high bandwidth, so while they can technically operate at 120 Hz, they don't exemplify the high-resolution capabilities typically associated with high-refresh-rate HDMI technology. 1440p can also provide high refresh rates, but it is not as commonly utilized in the context of high-resolution HDMI compared to 4K. Therefore, 4K at 120 Hz stands out as the correct and most appropriate answer in this scenario.