Sibelius File Format Page

Because .sib files store undo history and high-resolution graphics (if you’ve pasted in PNGs or SVG files), they can become bloated. A 10-page orchestral score might start at 200KB but balloon to 15MB after extensive editing.

Historically, Sibelius stored data in a highly compressed, memory-efficient manner—a design choice born from the limitations of early 1990s computer hardware (specifically the Acorn Archimedes). Even as the software migrated to Windows and Mac, the philosophy of efficiency remained. The binary nature of the file means that it cannot be opened or edited by a standard text editor; it requires the Sibelius parsing engine to decode the stream of data into visual notation. sibelius file format