.XLSB

Introduction

XLSB is a binary workbook format of Microsoft Excel, introduced with Excel 2007 alongside XLSX. It holds the same workbook as XLSX in the same kind of package, but writes each part as compact binary records instead of XML. Large workbooks open and save faster and take less space, which is why some people use it for big data sets. It can hold macros.

Microsoft publishes the format in full as [MS-XLSB].

Structure

An XLSB file is a ZIP package following the Open Packaging Conventions, laid out like XLSX, but its parts end in .bin: xl/workbook.bin, xl/worksheets/sheet1.bin, xl/sharedStrings.bin and xl/styles.bin. Each part is a sequence of records, each a record type and a size, both written as variable-length numbers, followed by the data. Some parts, such as the content types, relationships and document properties, stay XML.

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