Index: modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.202
diff -u -p -r1.202 system.install
--- modules/system/system.install	4 Dec 2007 16:39:22 -0000	1.202
+++ modules/system/system.install	6 Dec 2007 17:52:10 -0000
@@ -58,6 +58,16 @@ function system_requirements($phase) {
     $requirements['php']['severity'] = REQUIREMENT_ERROR;
   }
 
+  // Test PHP memory_limit
+  $requirements['php_memory_limit'] = array(
+    'title' => $t('PHP Memory Limit'),
+    'value' => ini_get('memory_limit') ? ini_get('memory_limit') : '',
+  );
+  if (ini_get('memory_limit') && parse_size(ini_get('memory_limit')) < parse_size(DRUPAL_MINIMUM_PHP_MEMORY_LIMIT)) {
+    $requirements['php_memory_limit']['description'] = $t('PHP memory of approximately %memory_limit is required for a Drupal core installation. You may need to increase this amount if using contributed modules.', array('%memory_limit' => DRUPAL_MINIMUM_PHP_MEMORY_LIMIT));
+    $requirements['php_memory_limit']['severity'] = REQUIREMENT_ERROR;
+  }
+
   // Test DB version
   global $db_type;
   if (function_exists('db_status_report')) {
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.559
diff -u -p -r1.559 system.module
--- modules/system/system.module	6 Dec 2007 09:58:33 -0000	1.559
+++ modules/system/system.module	6 Dec 2007 17:52:11 -0000
@@ -10,6 +10,7 @@ define('VERSION', '6.0-dev');
 define('DRUPAL_CORE_COMPATIBILITY', '6.x');
 
 define('DRUPAL_MINIMUM_PHP',    '4.3.3');
+define('DRUPAL_MINIMUM_PHP_MEMORY_LIMIT',    '16M');
 define('DRUPAL_MINIMUM_MYSQL',  '4.1.0'); // If using MySQL
 define('DRUPAL_MINIMUM_PGSQL',  '7.4');   // If using PostgreSQL
 define('DRUPAL_MINIMUM_APACHE', '1.3');   // If using Apache