Boolean storage takes up 1 byte?

Hi,

I've read the PostgreSQL documentation page on the boolean datatype (
http://www.postgresql.org/docs/8.4/static/datatype-boolean.html) to find out
what PostgreSQL's definition of a boolean is, as I believe it is distinctive
from a bit(1) datatype (as you can't max() a boolean.. not sure what an
efficient alternative to that is). However, I see that a boolean takes up 1
byte of storage, which is 8 bits. Is this due to the fact that the value
can be null? I'm not clear as to how a null field is stored, or is that the
point... nothing references is so it is defined as null? If that is the
case, can't this be stored as 1 bit? And does its storage as a byte affect
indexing or query planning?

Thom