Seen on an excellent blog, a Palm prototype. Yes, not an Apple prototype, but one from Palm. This is a model with a Retina display, meaning a higher resolution.
The first generations of Palm devices had a relatively low resolution (160 x 160), but with PalmOS 4, an equivalent to Retina was introduced: the High Density API. It works on the same principle: a higher resolution (320 x 320) and a mechanism to maintain compatibility with older applications. In practice, the text appeared finer, and apps were either rendered at 2x or adapted. Devices supporting this were quite rare under Palm OS 4, but the Wikipedia list seems comprehensive.
Dmitry’s prototype features a 320 x 320 display within a Palm m500 case. The m500 series at the time included three models: the m500 (monochrome), the m505 (color, with a mediocre display), and the m515 (the latter, improved). What Dmitry calls an m520 is marked « Fonts » and contains a beta version of Palm’s APIs. Essentially, it renders everything with text natively (with fine images) while everything else is upscaled. He explains the differences between this software and what was delivered in devices with high-resolution screens under Palm OS 4 (and integrated into Palm OS 5).
The Palm
The fine text
The test screen
The resolution marked inside
