specifics about BIT(n) types

please CC me as I'm on silent or digest.
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I know these questions have been asked, and once by me. I can't find it
in the archives or in the documentation.

1/ Are the bits in BIT(n) types stored as 1 bit per '0/1' or as one BYTE
per '0/1' ?
2/ What is the RANGE of the number of bits storable?
3/ What kind of speed comparisons are there between using BIT(n) tyeps
and using multiple columns of INT4/8 values?

For example:

SELECT bit_varying_128_A & bit_varying_128_B FROM some_table;
vs
SELECT int8_A & int8_B & int8_C & int8_C FROM some_other_table;

I sure would love to see the answers to these questions put in the
BIT(n) section of the USER MANUAL, section 5.9.