The size of NULL

How much space does NULLs take for different types?

What nullable types allocate space even when null?

http://social.msdn.microsoft.com/Forums/en/sqldatabaseengine/thread/dc168f01-075f-4f29-a669-eba93b4db6a0

Do columns occupy space even if they store NULL?

http://sankarreddy.spaces.live.com/blog/cns!1F1B61765691B5CD!387.entry

Space used for NULL

http://social.msdn.microsoft.com/Forums/en/sqlgetstarted/thread/e6b8abb8-851e-498d-93f0-2701f8e44b22

Null Values

http://msdn.microsoft.com/en-us/library/ms191504.aspx