There are different versions of Pinball Dreams with different video modes.
A Pinball Dreams demo version and Pinball Dreams Spanish version run in bog standard Mode 13h 320x200:
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The Pinball Dreams English version acquires a settings menu that can be entered from the table menu by pressing F5:
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If "High Res" is selected (that is the default in this version), the game runs in that weird tweaked video mode of theirs. It is not Mode X (unchained 320x240), but a vertically enhanced version, unchained 320x350 that they conjured up for the game:
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If "Low Res" is selected, then the game uses the Mode 13h 320x200 video mode as the demo and Spanish version above.
Pinball Fantasies shares this same low/high resolution setting in the game's setting menu, and applies these same video modes in the game with that setting.
The game is authored in square pixels.
As for hardware requirements, yeah, this game is very lightweight. It uses hardware scrolling to avoid needing to do heavy repaints, so even the crummy slow VGA graphics cards like Trident 8800CS and Oak Oti 037C are able to run this game at good performance.