Quick Answer
iPhone Duo uses a fixed 50:50 layout for two apps side by side; you cannot drag the divider to give one app more space in the launch experience.
Each half of the inner display closely matches the outer display’s size and proportions.
Zhong Wenze’s review connects this symmetry to the name “Duo,” the unfolding animation and the way content moves between screens.
The design favors consistent app shapes, but it sacrifices the flexibility of unequal split-screen windows.
Why Can’t You Resize Apps in iPhone Duo Split Screen?
The divider marks the boundary between two equal app spaces. Dragging it does not offer a one-third/two-thirds layout. If you searched for iPhone Duo split screen resize because that gesture seems broken, the behavior matches the fixed layout demonstrated in the review.
The useful question is why Apple settled on that arrangement. In Zhong Wenze’s iPhone Duo launch review, the explanation begins with the relationship between the outer screen and the two halves inside. His interpretation of the Duo name provides the starting point for the design analysis below.
The Duo Logic: One Screen Shape, Repeated
The review describes a 5.4-inch outer display and a 7.6-inch inner display, both using approximately √2:1 proportions when expressed as long edge to short edge. The full inner display is wider than it is tall in the side-by-side arrangement. Each half is taller than it is wide.
That change of direction matters. “The same ratio” does not mean every screen has the same width-to-height orientation. It means the rectangles share a shape after rotation. A-series paper uses the same geometric property: cut an A4-shaped rectangle into equal halves along its long dimension, and each half retains the original long-to-short ratio.
Why an equal split works
Start with an ideal inner rectangle measuring √2 units wide by 1 unit high. Each half is 1/√2 units wide by 1 unit high.
Half-screen long edge ÷ short edge = 1 ÷ (1/√2) = √2.
display
One compact canvas
Two matching canvases inside
So the inner display can act as one larger canvas or two familiar compact canvases. Zhong’s “four screens” framing refers to four useful display regions: the outer display, the complete inner display, and its left and right halves. Physically, there are still two display panels.
This makes “Duo” a compelling description of how the device works: the same basic canvas can be paired in several ways. It remains the reviewer’s reading of the product’s design and name.
What the Unfolding Animation Actually Explains
The review links the opening and closing transition to the Dock staying on the right. The animation makes the closed and open states feel spatially connected: the interface appears to continue into the larger display rather than jump into an unrelated layout.
Apple’s developer announcement also connects the matching display ratios with proportional scaling and smooth transitions between the outer and inner displays.
Visual continuity is different from a literal 1:1 pixel transfer
Outer display → one inner half: the destination is a similarly shaped, similarly sized app space.
Outer display → the full inner display: the destination is larger, and its orientation or interface arrangement may change.
Using the rounded 5.4-inch and 7.6-inch diagonals, geometrically similar full displays differ by about 1.41× in linear size and roughly 2× in area. That is proportional enlargement, not an identical-size copy.
The design benefit is a predictable visual handoff. Matching rectangles reduce one source of disruption, while the animation helps you understand where your content went. Keeping an article’s position, a draft or a video’s playback state still depends on the app’s behavior.
The right-side Dock also has a practical role in Zhong’s explanation: moving navigation away from the bottom preserves more vertical room on the short, wide cover display. That choice brings reachability compromises, discussed in our iPhone Duo one-handed use guide.
What Apple Gains—and What Users Lose—with 50:50
Our reading is that the fixed split makes the outer-screen canvas a reusable unit of the inner-screen experience. An app placed beside another app receives a shape it already needs to handle. That can make switching into multitasking more predictable.
The benefit: familiar space for both apps
Comparing two shopping pages, consulting a map beside a message, or dragging a photo into a conversation can work well when both apps receive equal room. The divider also stays aligned with the central fold.
The cost: equal space does not always match the task
A document may deserve most of the display while a chat needs only a narrow strip. A spreadsheet can benefit from more width than a reference note. Fixed halves make you accept the same allocation for both workflows.
The geometry explains the appeal of 50:50, but it does not make unequal splits technically impossible. In an ideal √2:1 inner rectangle, a two-thirds/one-third split would produce panels with long-to-short ratios of about 1.06:1 and 2.12:1. Neither retains the shared √2 shape.
Supporting those shapes would mean accommodating different layouts. Apple could choose that flexibility in software; the launch behavior prioritizes a smaller set of predictable arrangements. A coherent design can still feel restrictive when your two tasks need different amounts of space.
One Adaptation Helps Several Screens, but Does Not Finish the App
Zhong summarizes the opportunity as one adaptation benefiting three screens: the outer display and both inner halves. Read that as reuse of a common layout shape. It does not mean a developer can finish one screen and automatically deliver a polished foldable app.
His Xiaohongshu demonstration shows the difference. A picture can become immersive content, a video can sit beside comments, and rotation can change the viewing arrangement. These are decisions about what information belongs together, beyond simply enlarging the existing interface.
Two columns inside one app are different from two apps in Split View
A sidebar beside an article, or video beside comments, is an app’s own layout. The app can allocate its content internally. That does not give the user control over the system divider between two separate apps.
Apple’s multidisplay developer session describes layout tools, multiple app scenes and supplementary interfaces across displays. Those capabilities help developers build the experience; they do not remove the need to design navigation, keyboard behavior and folding transitions carefully.
This is where the geometric idea meets the broader iPhone Duo app optimization challenge: matching proportions can simplify the foundation, while useful large-screen layouts still require work.
Duo’s Paired-Screen Idea Goes Beyond Two Apps
The strongest part of Zhong’s interpretation is that the same relationship appears in several interactions. The review groups them into four types:
Inner half + inner half: two apps side by side, with drag-and-drop between supported apps. He also demonstrates linking an app pair so the two return together.
Outer display + full inner display: camera previews let people on opposite sides of the device see the shot.
Outer display + one inner half: his Duo FaceTime example lets people sitting on opposite sides of a table see a remote caller.
One angled half + the other: a partly folded device can separate content from controls, or present a clock and photos on the two inner regions.
These examples make the naming argument richer than “Duo means two apps.” The two sides can serve different tasks, different viewers or different viewing angles. Repeating the same proportions gives those pairings a common visual foundation.
It also explains why software and hardware feel tightly connected in the review. Screen shape, hinge position, navigation placement and transitions reinforce the same interaction model. The limitation appears when that model offers fewer arrangements than a particular task needs.
FAQ
Can iPhone Duo stack any two apps vertically?
In the launch behavior Zhong demonstrates, general two-app multitasking is side by side. He shows a separate video-and-app arrangement that places video above another app. That specialized layout does not establish a general top-and-bottom split for any two apps.
Does opening two windows of an app mean two independent accounts?
No. The review demonstrates two browser windows. Multiple windows are views supplied by an app; they do not automatically provide separate installations or independent account sessions. Account behavior depends on the app.
Would an app update unlock a movable system divider?
An update can improve how that app uses its allotted space. Changing the system’s fixed split would require Apple to change the multitasking behavior. The review provides no basis for promising such an update.
Related iPhone Duo Guides
- iPhone Duo Review Hub: Specs, Problems & Real-World Tests
- iPhone Duo’s App Ecosystem: Six Modes, One Uneven Experience
- iPhone Duo One-Handed Mode: Reachability and Grip Tips
- iPhone Duo Touch ID Is Slow: Unlock Delay Explained
- iPhone Duo Overheating During FaceTime and Beyond
- iPhone Duo Nano-Texture Film Removed: The Crease Revealed
- iPhone Duo Inner Screen Scratch Test Explained
Video: 钟文泽 (Zhong Wenze), iPhone Duo 首发评测：苹果的双屏奇谋. Review examples are based on the supplied transcript; geometric calculations and trade-off analysis are explained above. Software observations refer to the launch experience.
