History Lesson: What Is a .sxc File? OpenOffice Calc Spreadsheet

What is a .sxc file?

A .sxc file is a spreadsheet from OpenOffice.org Calc (and matching StarOffice Calc) during the OpenOffice.org XML era. The Internet media type is application/vnd.sun.xml.calc. UK National Archives PRONOM records fmt/129 for OpenOffice Calc 1.0 (also StarOffice Calc 6.0): a ZIP+XML package with external signature .sxc. OpenOffice.org’s XML FAQ lists .sxc as the Calc default for that generation. The Calc template sibling is .stc (application/vnd.sun.xml.calc.template). The same OpenOffice.org XML suite family also includes .sxw (Writer), .sxi (Impress), and .sxd (Draw) — this article is about Calc .sxc only.

The format sits between two better-known neighbors. Earlier StarOffice ~3–5 Calc used binary .sdc (StarCalc). Later OpenOffice.org 2.0 / StarOffice 8 moved to OpenDocument Spreadsheet (.ods) — an OASIS (Organization for the Advancement of Structured Information Standards) standard, later ISO/IEC 26300. OpenDocument is based on OpenOffice.org XML but is not the same package and is not directly compatible by renaming.

Origin in plain language: after Sun Microsystems acquired Star Division, Sun and the OpenOffice.org community pushed an XML-based office package around 2000–2002. StarOffice 6.0 (about May 2002, based on OpenOffice.org 1.0) made OpenOffice.org XML the default Calc path — .sxc on disk instead of the old binary StarCalc package. That mid-generation format is what still turns up on CDs, USB sticks, and “OpenOffice” folders labeled in the early–mid 2000s.

Is .sxc the same as .sdc or .ods?

No — and that three-way mix-up is why these legacy files keep landing in “what is this?” searches. .sdc is the older binary StarCalc / StarOffice Calc package from the StarOffice ~3–5 era. .sxc is OpenOffice.org XML: a ZIP of XML parts, default for StarOffice 6 & 7 and OpenOffice.org 1.x (~2002). .ods is OpenDocument Spreadsheet, which arrived with OpenOffice.org 2.0 / StarOffice 8 around May 2005 as the open-standard successor.

So the generation shift is: .sdc (binary StarCalc) → .sxc (OpenOffice.org XML package) → .ods (OpenDocument). Same product family over time; three different on-disk packages. OpenDocument grew out of OpenOffice.org XML, but a text editor and a rename will not turn a .sxc into a valid .ods. Changing .sxc to .sdc or .ods in Explorer does not convert anything.

Why won’t Excel open a .sxc file?

Microsoft Excel does not ship a built-in everyday importer for .sxc that typical users can rely on. Double-clicking a .sxc in 2026 fails as an unsupported format — not because the workbook is blank. You need a conversion path to a modern workbook such as XLSX or a values dump such as CSV. Do not expect every chart, macro, or edge-case formula to survive unchanged.

Descendants of the OpenOffice.org line — notably LibreOffice — still import legacy OpenOffice.org XML, which is why a .sxc that Excel refuses may still open in a free office suite. That import path is not the same as Excel “supporting” the format natively.

How the bytes work (ZIP+XML / OpenOffice.org XML)

On disk, a .sxc is a ZIP archive of XML and package parts — spell ZIP as the familiar compressed-folder container, and MIME as Multipurpose Internet Mail Extensions (the Internet media-type label). Inside you typically find an uncompressed mimetype file declaring application/vnd.sun.xml.calc, plus content.xml, styles.xml, meta.xml, settings.xml, and META-INF/manifest.xml, with optional embedded images and other parts. That package shape is why a hex dump can look “almost like” a later .ods — and why renaming still fails.

Contrast with the previous generation: many StarCalc .sdc files are OLE2 / compound binary packages (Object Linking and Embedding version 2 structured storage), not a ZIP of XML. Contrast with the next generation: .ods is OpenDocument’s ZIP+XML successor, standardized through OASIS and later ISO/IEC 26300. Same family story; different package contracts.

OpenOffice.org XML, OpenDocument, and why .sxc files still sit on disks

Free OpenOffice.org 1.x in the early–mid 2000s, school and home installs, NGO archives, and StarOffice 6/7 corporate deployments all saved Calc work as .sxc. Some migrations stopped at OpenOffice.org XML and never finished the later jump to .ods. CD and USB backups labeled “OpenOffice” still turn up in 2026 with budget sheets, class tables, and side projects that outlived the machines that created them.

An Excel window that refuses .sxc is not proof the workbook is empty. A ZIP listing that shows content.xml is not proof you can paste the cells into a modern sheet without a real conversion. These are legacy files from the middle generation of a product line that moved through binary StarCalc, OpenOffice.org XML, and OpenDocument.

Legacy File Converter lists OpenOffice Calc / .sxc (and .stc templates) among supported spreadsheets on Supported File Types and converts them locally on Windows to modern targets such as XLSX · CSV and related spreadsheet outputs. Nothing is uploaded — see also Convert Legacy Files Without CloudConvert. For the earlier binary StarCalc story, see History Lesson: StarCalc (.sdc); for Excel’s own binary lineage, see History Lesson: Excel .xls.