Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_57 ( sspec_number VARCHAR, i_o_bus VARCHAR )

### Question ###
What's the sSpec number of the processor having an ultra-low power I/O?

### Accurate SQL ###

SELECT sspec_number FROM table_name_57 WHERE i_o_bus = "ultra-low power"