Get read and write adapters in Magento

Copy/* @var $adapter Varien_Db_Adapter_Interface */
$adapter = Mage::getSingleton('core/resource')
    ->getConnection('core_read');

Copy/* @var $adapter Varien_Db_Adapter_Interface */
$adapter = Mage::getSingleton('core/resource')
    ->getConnection('core_write');