Thanks for reply. I use the same board with Winbond chip (32M), it can pass 150-160mhz. But use AS4C32M16SB-6TCN with it, it can only pass arround 90-100mhz. Don't know what's the problem. If board is bad, why Winbond chip can pass 150-160mhz ? It is strange. Maybe I buy the bad chip ?