Comment by canucker2016

MacWord 3.0+ (and then WinWord 1.1+) had fast-save which leaned on the in-memory piece-table data structure to write to disk only the changes to the Word document.

see https://web.archive.org/web/20160308183811/http://1017.songt...

The COM structured storage Office file format came from OLE2 (object linking and embedding - one of the mid-90s must-have features)