CREATE TABLE table_142573_1 (clock_rate__mhz_ NUMBER, designation VARCHAR2)

Name the least clock rate mhz when designation is rimm 4200
SELECT MIN(clock_rate__mhz_) FROM table_142573_1 WHERE designation = "RIMM 4200"
SELECT MIN("clock_rate__mhz_") FROM "table_142573_1" WHERE "RIMM 4200" = "designation"