I think that's decided by both the video card and the monitor.
Most LCD monitors are rated at 60Hz, and some will refuse to output anything higher e.g. 75Hz (showing "out of range").

If your monitor is capable of doing higher refresh rate you might have some luck with reprogrammable EDID dongles (and programmer) that you could write a custom default output timing with a supported resolution at 70Hz to override the values provided by the monitor. More modern video cards (likely since the generations on which DP1.2 becomes the norm, such as Radeon HD 7000 series, or nVidia Kepler family) seem to just use the default timing values specified in the EDID for default output, covering resolutions equal to or smaller than the one specified in the EDID.

PS: From my experience with my monitor, some ATi/AMD video cards (mostly Radeon HD 6000 series and before) appear to use 1152x864 at 75Hz by default (including while in DOS), without any EDID override. Your mileage may vary depending on your monitor model.

Is it running pure DOS or Win9x or under DOSBox emulation?

If it were dos emulation (i.e. DOSbox) it would skip the extra frames. This does sound like the symptoms I get when playing Lemmings on laptops with the 'high performance' option

I have an LCD monitor with a D-Sub connector that supports 75Hz and another with a DP connector that supports up to 144Hz. I would consider using a reprogrammable EDID dongle if they are available at a reasonable price.

I'm interested in hearing about running pure DOS, since DOSBox runs fine at 70Hz. I'm currently testing FreeDOS on an HP t620. "Univbe" doesn't work on it, so if it's a vBIOS issue, I'm considering purchasing a different model. I would greatly appreciate any information from anyone who owns a Wyse Cx0.

LSS10999 wrote on 2025-09-25, 14:24:

I think that's decided by both the video card and the monitor. Most LCD monitors are rated at 60Hz, and some will refuse to outp […]
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I think that's decided by both the video card and the monitor.
Most LCD monitors are rated at 60Hz, and some will refuse to output anything higher e.g. 75Hz (showing "out of range").

If your monitor is capable of doing higher refresh rate you might have some luck with reprogrammable EDID dongles (and programmer) that you could write a custom default output timing with a supported resolution at 70Hz to override the values provided by the monitor. More modern video cards (likely since the generations on which DP1.2 becomes the norm, such as Radeon HD 7000 series, or nVidia Kepler family) seem to just use the default timing values specified in the EDID for default output, covering resolutions equal to or smaller than the one specified in the EDID.

PS: From my experience with my monitor, some ATi/AMD video cards (mostly Radeon HD 6000 series and before) appear to use 1152x864 at 75Hz by default (including while in DOS), without any EDID override. Your mileage may vary depending on your monitor model.

I tried removing the 60Hz mode from the EDID emulator, and now Lemmings 2 runs successfully at 75Hz! Thank you so much for your help!