What value does a database use to represent NULL on disk?

When a database system writes a record to a page on disk, and one of the fields in that record is null, what value is used to represent that 'null' such that when the record is read back in, it knows that the field is 'null开发者_运维技巧.'

Perhaps it is dependent on the data-type of that field?

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It uses a NULL bitmap, you can use DBCC PAGE to take a closer look

Check out this link for more detail Poking about with DBCC PAGE