system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do photographs from 100 years ago look to be Hi-res and so clear; but pictures from the 60's seam so blurry and low detailed.
gpt
A hundred years ago, 135-film didn't exist. Instead, most pictures were shot on 120-film, or even larger film. A typical frame shot on 135-film is 36x24 mm, while a typical picture shot on 120-film is 60x60 mm (or larger, such as 60x90 mm). Even larger negatives were shot using large format cameras, 4x5 and 5x8 inches are common large format frame sizes. 

The film has a specific "resolution" (with film, the achievable resolution mainly depends on the grain size), increasing the area also increases the total achievable resolution.