Computed field storage for SQL?

Is the value of a computed field calculated only on need, or is it stored permanently? For instance, if you have a table for addresses:

CREATE TABLE Address
(
id int NOT NULL IDENTITY (1,1),
street varchar(50) NOT NULL,
city varchar(50) NOT NULL,
state varchar(2) NOT NULL,
zip varchar(10) NOT NULL,
mailingText AS street +CHAR(10)+ city +', '+ state +' '+ zip
)

is mailingText taking up table space, or just recordset space?

That should be recordset space only....from the microsoft sql server 2000 books online :

beautifull. So, if I don't request this column, (for instance,
SELECT street, city, state, zip
FROM Address
WHERE state = 'CA') is the value not calculated?
I've got potentially a massive count of Address records, and need to know what efficiencies using computed fields hits.

Thanks