xls The .xls filename extension is a native binary file format associated with the closed source spreadsheet application Microsoft Office Excel. First introduced in 1987 with the release of Excel 2.x, the file format acts as the container for storing spreadsheet data such as work sheets, charts, and macros. Prior to Microsoft Office Excel 2007, the xls binary format was the default standard for the Microsoft Office Excel until the later adoption of the Open Document standard .xlsx. Documents to be saved in the .xls format are saved as Excel 97, 2003 documents.
csv The comma-separated values file format or CSV for short is a common cross platform file format used for information exchange between disparate devices, systems, and software. Mainstream usage of the format begun in 2005, with RFC 4180 forming the basis of its specification. The format's strongest feature is the ability to store relational tabular data in a plain text format which can be imported and/or exported to any compatible application. Because of this feature and the relatively small file size, CSV is commonly used for exporting and importing data from populated databases or spreadsheet files that use a proprietary format, to other systems and applications that utilize different file formats and architectures. The csv format is limited though in its inability to represent records only from a relational data source. It does not support object oriented or hierarchical databases.