user: ### NOW ANSWER:
Question: What shows for Southbridge when the Model number is AMD-640 chipset?
Columns: ['Model', 'Code name', 'CPU support', 'FSB / HT (MHz)', 'Southbridge']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['AMD-640 chipset', 'AMD-640', 'K6 , Cyrix 6x86', '66 (FSB)', 'AMD-645']
SQL:

assistant: SELECT "Southbridge" FROM "Table" WHERE "Model" = 'AMD-640 chipset';