[bbanyc]

A while back I read a piece by, I think, Joel Spolsky on the "design" of the XLS format. It was mostly a dump of Excel's internal memory structures to disk, with some optimizations to speed up saving and loading on the slow disks of the time. He seemed quite satisfied with how well the software performed but all I was thinking is "any other program trying to deal with those files is screwed." And "any other program" includes later versions of Excel.

It'd be nice to have some documentation of the internals of old DOC and XLS formats, just for the sake of recovering old files for archival purposes, but it's likely that Microsoft never bothered documenting them, even internally.

[happymellon]

This is also true of DOC. It was just a dump of the internal representation of Word.

Hence why they had to completely overhaul it with DOCX/XLSX when we had the open standards requirements come in. There was no possible way for Microsoft to document it. Although it doesn't help that DOCX/XLSX have tags for "Internal binary dump of Word/Excel" so they also fall into the same trap.

[rrr_oh_man]

YES, it's an excellent read!

https://www.joelonsoftware.com/2008/02/19/why-are-the-micros...

[davidgerard]

Microsoft has in fact documented these old formats, because they were forced to in antitrust actions!

Per Spolsky, they're an absolute shower. But they are, technically, documented!

[mjburgess]

They would, presumably, just need to release the header files?

All file formats are, in the end, just memory structures written in binary.

[anticensor]

Then their dark history would have been obvious.