+if ( is_blog_installed() ) {
+ display_header();
+ die( '<h1>' . __( 'Already Installed' ) . '</h1><p>' . __( 'You appear to have already installed WordPress. To reinstall please clear your old database tables first.' ) . '</p><p class="step"><a href="../wp-login.php" class="button">' . __('Log In') . '</a></p></body></html>' );
+}
+
+$php_version = phpversion();
+$mysql_version = $wpdb->db_version();
+$php_compat = version_compare( $php_version, $required_php_version, '>=' );
+$mysql_compat = version_compare( $mysql_version, $required_mysql_version, '>=' ) || file_exists( WP_CONTENT_DIR . '/db.php' );
+
+if ( !$mysql_compat && !$php_compat )
+ $compat = sprintf( __('You cannot install because <a href="http://codex.wordpress.org/Version_%1$s">WordPress %1$s</a> requires PHP version %2$s or higher and MySQL version %3$s or higher. You are running PHP version %4$s and MySQL version %5$s.'), $wp_version, $required_php_version, $required_mysql_version, $php_version, $mysql_version );
+elseif ( !$php_compat )
+ $compat = sprintf( __('You cannot install because <a href="http://codex.wordpress.org/Version_%1$s">WordPress %1$s</a> requires PHP version %2$s or higher. You are running version %3$s.'), $wp_version, $required_php_version, $php_version );
+elseif ( !$mysql_compat )
+ $compat = sprintf( __('You cannot install because <a href="http://codex.wordpress.org/Version_%1$s">WordPress %1$s</a> requires MySQL version %2$s or higher. You are running version %3$s.'), $wp_version, $required_mysql_version, $mysql_version );
+
+if ( !$mysql_compat || !$php_compat ) {
+ display_header();
+ die('<h1>' . __('Insufficient Requirements') . '</h1><p>' . $compat . '</p></body></html>');
+}