the short version

If you want to play Windows games on a vertical monitor with the lowest possible latency (“input lag”), and don’t feel like testing anything out:

• Use Windows 11. It has a better CPU scheduler, and game optimizations that other versions don’t.
• Check your graphics drivers for latency-related settings, like NVIDIA’s “Low Latency Mode” and “Vulkan/OpenGL present method”.
• Don’t rotate your monitor in Windows. Leave it in its default orientation.
• Set the monitor you use for games as your “primary” monitor in Windows.
• In game settings, use “Exclusive Fullscreen” or the option that sounds the closest.
• Use in-game rotation settings to rotate the screen.

This makes no intuitive sense, but I promise it’s real, at least on some systems: not all GPUs can use fast presentation modes (or variable refresh rate!) while Windows display rotation is active. If you’d like to test this for yourself, try PresentMon or Special K.

the longer version

Your Windows¹ PC has something called a “compositor”. When a program on your PC generates an image to show you, the compositor puts that image in a window, then arranges windows as you drag and refocus them.² This is a slow process: the compositor adds display latency.

When you play a game on your PC, it’ll usually ask you whether you want to play in “Fullscreen”, “Borderless Fullscreen”, or “Windowed”. Different developers sometimes use different terms for these,³ so I’ll define some terms.

• Windowed: It draws in a regular window.
• Exclusive Fullscreen: The kind of fullscreen that sometimes makes it annoying to alt-tab. Not all programs have this: some only have Borderless Fullscreen.
• Borderless Fullscreen: The kind of fullscreen that lets you alt-tab without annoying you. (Actually just a big window without a title bar or border.)

Exclusive Fullscreen has the lowest latency, since it draws directly to the screen without using the compositor: this is why it’s annoying to alt-tab sometimes. Windowed and Borderless Fullscreen both use the compositor, so they have higher latency.

However, on modern systems, modern software can use special features of your graphics card to skip the compositor. This depends on your operating system, graphics card, graphics drivers, the game, and the size of the game window, but the practical upshot is simple:

On a Windows 10/11⁴ system with a modern graphics card, some games can use Borderless Fullscreen without adding compositor latency. Even for games that aren’t new or smart enough to do this, Windows will try to help them do it anyway.⁵

However, in order to use “fast” Borderless Fullscreen, these games usually need to meet very specific conditions.⁶

• The game must use a specific graphics API.⁷:
• The game must be on your primary monitor.
• Nothing can be in front of the game.⁸
• The game must be the exact same resolution as your primary monitor.

That last condition is the problem. Windows display rotation changes the resolution your games run in, but not the “real” resolution of your monitor. That means if your GPU doesn’t have the right features⁹, the compositor has to rotate the game to match your Windows settings, and “fast” Borderless Fullscreen can’t be used.

Not every game has Exclusive Fullscreen. Even for the ones that do, Windows will sometimes try to convert them to “fast” Borderless Fullscreen. So to guarantee the lowest latency, we need to make sure that the conditions for “fast” Borderless Fullscreen are always met.

If you don’t have the tools or time to check, better safe than sorry: use in-game rotation options, not Windows monitor rotation!

the tools to check

PresentMon is Intel’s weird GPU monitoring software. It can be configured to check “presentation mode”, which is what actual graphics programmers call the the thing we’ve been talking about.

After configuring PresentMon to add a “Present Mode” entry to the overlay…

…and changing the overlay to a separate window in “Settings”, to avoid stacking on top of the game and changing its presentation behavior…¹⁰

…you can select any running game from the “Process” dropdown on the main page. Ignore the FPS display and any other gauges; we’re looking for “Present Mode”.

Presentation modes starting with “Hardware” or “Hardware Composed” are fast. Presentation modes starting with “Composed” use the compositor, and add extra latency. If you’re curious about whether monitor rotation affects your setup, test for yourself!