What do you know about multi threaded calculation?
Excel 2007 can split calculation across multiple processors or cores. When Excel 2007 loads a workbook, it determines from the operating system how many processors are available and then creates a separate calculation thread for each processor. These threads can then run in parallel. The beauty of this system is that it scales extremely well with the number of processors.
Most workbooks show a significant improvement in calculation speed on a system with multiple cores. The degree of improvement depends on how many independent calculation trees the workbook contains. If you make a workbook that contains one continuous chain of formulas, it will not show any multithreaded calculation (MTC) performance gain, whereas a workbook that contains several independent chains of formulas will show gains close to the number of processors available.