When should the xlsm or xlsb formats be used?

Question

Since Excel 2007, Microsoft has split the classical .xls format to several formats (in particular, .xlsx, .xlsm, .xlsb).

Answer 1

Just for posterity, here's the text from several external sources regarding the Excel file formats. Some of these have been mentioned in other answers to this question but without reproducing the essential content.

1. From Doug Mahugh, August 22, 2006:

...the new XLSB binary format. Like Open XML, it’s a full-fidelity file format that can store anything you can create in Excel, but the XLSB format is optimized for performance in ways that aren’t possible with a pure XML format.

The XLSB format (also sometimes referred to as BIFF12, as in “binary file format for Office 12”) uses the same Open Packaging Convention used by the Open XML formats and XPS. So it’s basically a ZIP container, and you can open it with any ZIP tool to see what’s inside. But instead of .XML parts within the package, you’ll find .BIN parts...

This article also refers to documentation about the BIN format, too lengthy to reproduce here.

2. From MSDN Archive, August 29, 2006 which in turn cites an already-missing blog post regarding the XLSB format:

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 size – file size of both formats is approximately the same, since both formats are saved to disk using zip compression Architecture – both formats use the same packaging structure, and both have the same part-level structures. Feature support – both formats support exactly the same feature set Runtime performance – once loaded into memory, the file format has no effect on application/calculation speed Converters – both formats will have identical converter support