A4-like screen sizes for tablets

The A0, A1... A5 paper sizes are defined with a length to width ratio of sqrt(2), so that when you tear one sheet into two the smaller sheets have the same length-to-width ratio.

A big drawback of non-windowed operating systems for tablets (like the one on the iPad) is that they make it impossible to interact with more than one app at a time. For example, it would be convenient to copy something from a webpage to a document, by opening them both side by side and dragging stuff from one to the other - but this isn't possible with only full-screen apps.

You would rarely need to interact with more than two applications at the same time, so I think a split-screen side-by-side view would suffice in the vast majority of use cases.

Of course, much of the time you would still want to run your applications full screen. This would require most app writers to support two different modes - full screen and split screen, which is extra work.

A tablet computer which has a screen with a length-to- width ratio of sqrt(2) would eliminate this problem, because now when the user enters side-by-side mode, the operating system can simply shrink the app uniformly to take just half the screen.

It's true that fonts will become smaller, but only by about 29%. If the app uses at least 11 point font while in full screen, I think text would still be readable (just a little under 8pt) while in side-by-side mode.

The aspect ratio 1.414 is between standard (1.333) used by the iPad and all, and widescreen (1.78), so it would be quite natural to use. While watching widescreen video there will be some letterboxing (but not as much as on a standard screen), and for standard aspect video there would be black bars on the sides (but not as much as on a widescreen)

A real A4 sized display would be about 14" across, but this could be a smaller device as well, as long as the ratio is sqrt(2). I think a good resolution to have is 1154 * 816 (very low error rounding to integer pixels).