看到「DPI Calculator / PPI Calculator」這個網站，裡面有一些有趣的小螢幕，但是有超高解析度：
1280x1024 @ 0.61 MicroOLED microdisplay (2687.21 PPI)
1920x1080 @ 0.74 Silicon Micro Display ST1080 (2976.9 PPI)
2048x1536 @ 0.83 Forth Dimension QXGA-R9 (3084.34 PPI)
2048x2048 @ 0.99 Kopin Lightning 2K (2925.57 PPI)
不過如果放寬到只要是螢幕就可以的話 (不用是彩色的)，查了一下發現跟目前的進展有點遠，目前有查到的是 14000 DPI：「14,000ppi MicroLED display is world’s densest, only 0.48mm across」：
According Mojo Vision, with a world record pixel pitch of 1.8µm and a pixel density over 14,000ppi, the monochrome display technology is the company’s first important step in succeeding in its mission to deliver “Invisible Computing”, enabling people to receive and share information that is immediate and relevant without distracting them from the world in front of them.
不過考慮到彩色螢幕需要三色，上面那幾個 3000 PPI 好像已經很厲害了...