How does SQL server compress NULL bit datatypes? [duplicate]

Question

Possible Duplicate:
Can Microsoft store three-valued fields in a single bit?

According to the documentation for bit, the bit datatype can have three values, 0, 1 and NULL and if there are 8 or less bit columns in a table, those columns will be compressed into one byte.

These two behaviors seem contradictory. If so, which part is correct, the ability of a bit to be NULL or the compression of 8 bits to a byte?

Answer 1

NULL values are handled by a separate bit for each column (for example look here for details).