This section is only relevant to users of Excel 2010.
Excel 97 through 2007 were all 32-bit applications, even when run on a 64-bit edition of Windows.
Excel 2010 has both 32-bit and 64-bit editions, and although the 64-bit edition requires a 64-bit version of Windows, the 32-bit edition can be run in both 32-bit and 64-bit Windows.
Why all this talk of bits? A significant end result for the user is that the 64-bit edition of Excel can open much bigger workbooks.
OAK also comes in both 32 and 64-bit editions. The edition of OAK that is used must match the edition of Excel that is used.
The 64-bit edition of OAK is only required if you are using the 64-bit edition of Excel.
Which edition of Excel 2010 am I using?
To find out which edition of Excel 2010 you are using, click File | Help and look on the right of the window.
Excel 2010 32-bit
Excel 2010 64-bit