Explainer

Borderless vs exclusive fullscreen: why overlays only work in one of them

Every game's video settings offer some flavor of borderless vs exclusive fullscreen, most people pick whatever was default, and almost nobody knows what the setting actually changes. But it's the single switch that decides whether anything — a picture-in-picture video, a second app, a terminal overlay running your coding agent — can appear over your game. Here's what each mode really does.

Exclusive fullscreen: the game owns the display

In exclusive (or "true") fullscreen, the game takes direct control of the display. Its frames go more or less straight to the screen, bypassing the operating system's compositor — the part of the OS that normally stacks all your windows into one picture. That bypass was the whole point: in the 2000s it meaningfully reduced latency and raised frame rates, which is why "fullscreen = faster" became gospel.

The cost is that the OS is locked out of its own screen. Nothing else can be drawn — no notifications, no volume popup, no overlay windows. Alt-tab forces a jarring mode switch: black screen, resolution flicker, sometimes a crashed game.

Borderless: a window in a trench coat

Borderless fullscreen (also called "borderless windowed" or "windowed fullscreen") is just a normal window with no title bar, sized exactly to your screen. It looks identical to fullscreen, but it lives inside the compositor like every other window. That means:

• Instant alt-tab — no mode switch, no black flash.
• Notifications and popups work — the OS can draw over the game.
• Always-on-top windows work — which is the mechanism overlays like Backgrind use.
• Multi-monitor behaves — your mouse can leave the screen without minimizing the game.

The performance myth

The "exclusive is faster" rule is mostly a fossil. Since Windows 10's fullscreen optimizations and the DXGI flip presentation model, a borderless game that covers the whole screen gets promoted to an "independent flip" path — effectively the same direct route to the display that exclusive mode used, while still letting the compositor interject when something needs to draw on top. On Windows 11 this is the default behavior, and for most modern titles the difference in frame rate and input latency is within noise.

The exceptions are old DX9-era games and some edge cases with VRR/G-Sync, where exclusive mode can still behave differently. If you play one of those competitively, test both. For everything else, borderless costs you nothing you can measure.

Why overlays only work over borderless

An always-on-top window is drawn by the compositor: when the OS assembles the screen, it stacks that window above the others. In exclusive fullscreen there is no stack — the game's frames bypass composition entirely, so there's nowhere for another window to go. That's why a plain overlay window simply can't appear over exclusive fullscreen, no matter what it does.

The alternative — injecting code into the game to draw inside its frames, the way the Steam overlay works — does function in exclusive mode, but it means entering the game process, which is exactly the behavior anti-cheat watches for. We covered that trade-off in "Will a coding overlay get me banned?" — short version: Backgrind stays a plain window on purpose, and asks for borderless instead.

How to switch (ten seconds)

1. Open your game's Video / Graphics / Display settings.
2. Find Display Mode (sometimes "Window Mode").
3. Pick Borderless — naming varies: "Borderless Window" (most games), "Windowed Fullscreen" (WoW, Overwatch), "Borderless Windowed" (Cyberpunk).
4. Confirm the resolution matches your display's native resolution.

Practically every modern title has the option — WoW, League, Dota 2, Fortnite, Baldur's Gate 3, Path of Exile, Elden Ring. Many newer games don't even offer exclusive mode anymore, which tells you where the industry landed.

The takeaway

Borderless gives you the same picture, near-identical performance on modern Windows, instant tabbing — and a screen the OS can actually draw on. That last part is what makes it possible to keep an AI coding agent visible in the corner while you play. See it in action in the live demo.