Index: ./modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.263
diff -u -p -r1.263 system.install
--- ./modules/system/system.install	6 Sep 2008 08:36:21 -0000	1.263
+++ ./modules/system/system.install	8 Sep 2008 05:46:47 -0000
@@ -92,6 +92,18 @@ function system_requirements($phase) {
     }
   }
 
+  // Test for PDO extension
+  if ($phase == 'install') {
+    if (!extension_loaded('pdo') || !class_exists('PDO')) {
+      $requirements['pdo'] = array(
+        'title' => $t('PDO library'),
+        'value' => $t('Not found'),
+        'severity' => REQUIREMENT_ERROR,
+        'description' => $t('Your PHP configuration does not include the required PDO extension. See <a href="@url">@url</a> for more information on how to configure PDO.</a>', array('@url' => 'http://www.php.net/pdo')),
+      );
+    }
+  }
+
   // Test DB version
   global $db_type;
   if (function_exists('db_status_report')) {