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To this point in the blog, I haven't talked too much about the file formats that Excel 2007 uses, since Brian Jones has been covering the new Office Open XML format pretty well in his blog. Today I thought I'd give an overview of the three main formats that we have in Excel 2007.
File Format Number 1 - Office Open XML (XLSX, XLSM, XLTX, XLTM, and XLAM files)The Office Open XML format is a full fidelity (all features of the product are supported) file format for Excel 2007, and it is the default file format that Excel uses to save new files. These files are composed of several XML parts, all bundled within a zip-compressed file for efficient storage. Brian has done a pretty good job of covering the Office Open XML format, and one of my posts a while back listed additional resources if you want to know more about the internals of the format.
To recap a bit, here are some of the interesting bits about this format:
File Format Number 2 - Excel Binary (XLSB files)The Excel binary format is the second full fidelity format for Excel 2007. It is similar to the Office Open XML format in structure - a set of related parts, in a zip container - except that instead of each part containing XML, each part contains binary data.
Even though we've done a lot of work to make sure that our XML formats open quickly and efficiently, this binary format is still more efficient for Excel to open and save, and can lead to some performance improvements for workbooks that contain a lot of data, or that would require a lot of XML parsing during the Open process. (In fact, we've found that the new binary format is faster than the old XLS format in many cases.) Also, there is no macro-free version of this file format – all XLSB files can contain macros (VBA and XLM). In all other respects, it is functionally equivalent to the XML file format above:
File Format Number 3 - Excel 97-2003 (XLS, XLT, and XLA files)The last format I'll talk about is the format that everyone is the most familiar with - our binary XLS file format from current versions of Excel. This format still exists in Excel 2007, and Excel can save many of the new Excel 2007 features into this format (though only Excel 2007 can view these features - they are not available in earlier versions of Excel). However, while XLS can still be used in a mixed-Excel environment to share files between users of Excel 2007 and earlier Excel versions, XLS is no longer a full fidelity format for Excel 2007. With many of the increased limits and new functionality we added, it became apparent that this format just couldn't scale to meet our needs - hence the move to the formats discussed above. When users save spreadsheets to this format, if those spreadsheets contain features not supported by the format, they will be presented with a "Compatibility Checker" dialog, alerting them to the functionality that is lost or degraded when the file is saved into the XLS format.
Using the Compatibility Checker, users can get help on many of the issues or navigate to the location in the spreadsheet where the offending feature is used in order to better understand the impact of saving into the XLS file format.
Working with Excel ServicesThe last thing I wanted to touch on is our file format support in Excel Services. Users can publish files to Excel Services using either the XLSX format or the XLSB format (as long as there are no macros) and expect the same level of functionality from their workbooks running on the server - though, as I have mentioned, not all Excel features are supported in the first release of Excel Services.
So what format should I use?Good question ... our guidance is as follows:
Hopefully that clears up the various formats that we've got for Excel 2007 - I encourage you to try each of the formats and send any feedback that you have.
Where is the best place to report this as a request to get this fixed..