Open XLS File

XLS File Format

Information in XLS files is stored in binary format. It is impossible to get any information by looking into XLS file in text editor. You either will need to have a Microsoft Excel or another application which can open XLS files installed or be able to parse binary code structures using HEX editor. Below we give a brief introduction into XLS file structure. For in depth information refer to corresponding documentation on XLS file format in our links section.

XLS files utilize CFBF (Compound File Binary Format) to store information. CFBF is a container file format which internally resembles a disk with a file system stored within a file. Files in CFBF format are capable of storing multiple files and streams within one file. CFBF was developed by Microsoft to use in Microsoft COM Structured Storage and later was adopted for other uses in Microsoft products including Microsoft Office documents. Information in CFBF file is stored in sectors which are addressed using File Allocation Table which defines how sectors are linked to each other. Information about streams and directories within the file is stored in stream and directory sectors correspondingly.

Each XLS file has a stream named Workbook in a root CFBF directory. Different XLS file versions may have this stream named as Worksheet or Workspace. Root Workbook stream is divided into several parts which describe workbook global variables and stored worksheets. Worksheet streams are divided into records. Each record contains specific information about features of the document or its content. Each record consists of a header with the record type and size, followed by the record data. Records can store various types of information like RGB colors, RK values, Unicode strings, error codes, constant values, border line styles, formulas and many more. For example RK values store integer or floating values located in the cell and formulas store Excel formulas used to calculate values on the fly.

XLS file format provides many important features which allow storing of complex information within the file. Up to Microsoft Office 2010 XLS was the main storage format used for spreadsheets in Microsoft Office. But Starting with Microsoft Office 2013 it was replaced by XLSX which stores information in Office Open XML format - an open format based on XML. XLSX format allows easier debugging, integration into enterprise workflows and distribution.

For more information about XLS format details refer to https://www.openoffice.org/sc/excelfileformat.pdf.