[sheetjs]

> Presumably Excel has to load everything into memory at once since it's immediately viewable, right?

Depends on the file format. An XLS or XLSB file can contain special markers for where each logical row starts, so it can randomly access rows; Both also can persist "calculation chains, which are a simplified dependency graph. The binary formats also store formulae in a parsed representation allowing easy scans to see what cells have to be inspected if a file needs to be recalculated.

[MooMooMilkParty]

Aha! As far as persisting calculations, this makes sense. I guess in my head I was thinking "pure" data where everything opened was precomputed. Forgive my ignorance about database solutions, but do they not implement something similar?

But now you've got me thinking, it would be nice if libraries like Dask could allow for flagging of symbolic operations like this to be written to disk for quickly saving metadata where intermediate steps don't explicitly need to be saved.