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Title: Excel 2007 XLL SDK is released!

Today’s author: Danny Khen, a program manager on the Excel team who works in the areas of programmability and business intelligence.  Danny worked with a number of people, both internal and external, on the Excel 2007 XLL SDK. 

The Microsoft Office Excel 2007 XLL Software Development Kit is out the door at long last. Many Excel developers have been waiting for the new XLL SDK for a long time now, since we released Office 2007 at the end of last year. It took us longer than we had initially thought to update the SDK content and develop the new documentation, and as an interim measure we handed out a release candidate of the core API files to folks who asked for it. We hope that you will find the wait was worthwhile, and will be satisfied with the quality of the final SDK we’ve just released – the API files, the framework and code samples, and of course the extensive and detailed documentation.
 
Please find the new SDK here:

  1. Download: http://www.microsoft.com/downloads/details.aspx?familyid=5272e1d1-93ab-4bd4-af18-cb6bb487e1c4&displaylang=en
  2. Online documentation: http://msdn2.microsoft.com/en-us/library/bb687883.aspx 

Excerpt from the SDK documentation:
 
The Microsoft Office Excel 2007 XLL Software Development Kit is designed to help you understand the relevant concepts and technologies that relate to creating DLL add-ins for Microsoft Office Excel 2007 that use the Excel C API. The C API enables DLLs to be integrated tightly with Excel 2007 and to access the internal functionality in Excel. These DLL add-ins are known as XLLs, given that they are usually given the file name extension .xll.
The primary reason for writing XLLs and using the C API is to create high-performance worksheet functions. Although XLL functions are frequently referred to as user-defined functions, the investment in time to obtain the understanding and skills that are required to write XLLs make this a technology impractical for most users. Nevertheless, the applications of high-performance functions—and, in Excel 2007, the ability to write multithreaded interfaces to powerful server resources—make it a very important part of Excel extensibility. The performance of XLLs is further enhanced in Excel 2007 by the addition of new data types and, most important, support for multithreading.

The Excel 2007 XLL Software Development Kit contains a framework library that is designed to speed up the writing of XLLs, and also three sample projects.

PS Edited to add post author information