thanks All, I got it. The extension_dir was set c:\php\extentsion instead of "c:\php\ext".
after fixing it, phpinfo() shows both mysql and myslqi see below
mysql
MySQL Support enabled
Active Persistent Links 0
Active Links 0
Client API version mysqlnd 5.0.10 - 20111026 - $Id: e707c415db32080b3752b232487a435ee0372157 $
Directive Local Value Master Value
mysql.allow_local_infile On On
mysql.allow_persistent On On
mysql.connect_timeout 60 60
mysql.default_host no value no value
mysql.default_password no value no value
mysql.default_port no value no value
mysql.default_socket no value no value
mysql.default_user no value no value
mysql.max_links Unlimited Unlimited
mysql.max_persistent Unlimited Unlimited
mysql.trace_mode Off Off
mysqli
MysqlI Support enabled
Client API library version mysqlnd 5.0.10 - 20111026 - $Id: e707c415db32080b3752b232487a435ee0372157 $
Active Persistent Links 0
Inactive Persistent Links 0
Active Links 0
Directive Local Value Master Value
mysqli.allow_local_infile On On
mysqli.allow_persistent On On
mysqli.default_host no value no value
mysqli.default_port 3306 3306
mysqli.default_pw no value no value
mysqli.default_socket no value no value
mysqli.default_user no value no value
mysqli.max_links Unlimited Unlimited
mysqli.max_persistent Unlimited Unlimited
mysqli.reconnect Off Off