CREATE TABLE table_21020 ("Model number" TEXT, "sSpec number" TEXT, "Frequency" TEXT, "GPU frequency" TEXT, "L2 cache" TEXT, "I/O bus" TEXT, "Memory" TEXT, "Voltage" TEXT, "TDP" TEXT, "Socket" TEXT, "Release date" TEXT, "Part number ( s ) " TEXT, "Release price  (  USD  ) " TEXT)

Name the memory for meodel number for atom e640t
SELECT "Memory" FROM table_21020 WHERE "Model number" = 'Atom E640T'
SELECT "Memory" FROM "table_21020" WHERE "Model number" = 'Atom E640T'