CREATE TABLE table_21017 ("Model number" TEXT, "sSpec number" TEXT, "Frequency" TEXT, "L2 cache" TEXT, "FSB" TEXT, "Mult." TEXT, "Voltage" TEXT, "TDP" TEXT, "Socket" TEXT, "Release date" TEXT, "Part number ( s ) " TEXT, "Release price  (  USD  ) " TEXT)

Name the fsb for atom z540
SELECT "FSB" FROM table_21017 WHERE "Model number" = 'Atom Z540'
SELECT "FSB" FROM "table_21017" WHERE "Model number" = 'Atom Z540'