Where does drupal store content-type display settings?
By Default it stores in field_config_instance table.. For relevant code check below function in field.crud.inc file

function _field_write_instance($instance, $update = FALSE) {
  $field = field_read_field($instance['field_name']);
  $field_type = field_info_field_types($field['type']);

  // Set defaults.
  $instance += array(
    'settings' =&gt; array(),
    'display' =&gt; array(),
    'widget' =&gt; array(),
    'required' =&gt; FALSE,
    'label' =&gt; $instance['field_name'],
    'description' =&gt; '',
    'deleted' =&gt; 0,
  );

  // Set default instance settings.
  $instance['settings'] += field_info_instance_settings($field['type']);

  // Set default widget and settings.
  $instance['widget'] += array(
    // TODO: what if no 'default_widget' specified ?
    'type' =&gt; $field_type['default_widget'],
    'settings' =&gt; array(),
  );
  // If no weight specified, make sure the field sinks at the bottom.
  if (!isset($instance['widget']['weight'])) {
    $max_weight = field_info_max_weight($instance['entity_type'], $instance['bundle'], 'form');
    $instance['widget']['weight'] = isset($max_weight) ? $max_weight + 1 : 0;
  }
  // Check widget module.
  $widget_type = field_info_widget_types($instance['widget']['type']);
  $instance['widget']['module'] = $widget_type['module'];
  $instance['widget']['settings'] += field_info_widget_settings($instance['widget']['type']);

  // Make sure there are at least display settings for the 'default' view mode,
  // and fill in defaults for each view mode specified in the definition.
  $instance['display'] += array(
    'default' =&gt; array(),
  );
  foreach ($instance['display'] as $view_mode =&gt; $display) {
    $display += array(
      'label' =&gt; 'above',
      'type' =&gt; isset($field_type['default_formatter']) ? $field_type['default_formatter'] : 'hidden',
      'settings' =&gt; array(),
    );
    if ($display['type'] != 'hidden') {
      $formatter_type = field_info_formatter_types($display['type']);
      $display['module'] = $formatter_type['module'];
      $display['settings'] += field_info_formatter_settings($display['type']);
    }
    // If no weight specified, make sure the field sinks at the bottom.
    if (!isset($display['weight'])) {
      $max_weight = field_info_max_weight($instance['entity_type'], $instance['bundle'], $view_mode);
      $display['weight'] = isset($max_weight) ? $max_weight + 1 : 0;
    }
    $instance['display'][$view_mode] = $display;
  }

  // The serialized 'data' column contains everything from $instance that does
  // not have its own column and is not automatically populated when the
  // instance is read.
  $data = $instance;
  unset($data['id'], $data['field_id'], $data['field_name'], $data['entity_type'], $data['bundle'], $data['deleted']);

  $record = array(
    'field_id' =&gt; $instance['field_id'],
    'field_name' =&gt; $instance['field_name'],
    'entity_type' =&gt; $instance['entity_type'],
    'bundle' =&gt; $instance['bundle'],
    'data' =&gt; $data,
    'deleted' =&gt; $instance['deleted'],
  );
  // We need to tell drupal_update_record() the primary keys to trigger an
  // update.
  if ($update) {
    $record['id'] = $instance['id'];
    $primary_key = array('id');
  }
  else {
    $primary_key = array();
  }
  drupal_write_record('field_config_instance', $record, $primary_key);
}


It stores in above table data column as blob format... Sample example goes below inside blob..

a:6:{s:5:"label";s:7:"Comment";s:8:"settings";a:2:{s:15:"text_processing";i:1;s:18:"user_register_form";b:0;}s:8:"required";b:1;s:7:"display";a:1:{s:7:"default";a:5:{s:5:"label";s:6:"hidden";s:4:"type";s:12:"text_default";s:6:"weight";i:0;s:8:"settings";a:0:{}s:6:"module";s:4:"text";}}s:6:"widget";a:4:{s:4:"type";s:13:"text_textarea";s:8:"settings";a:1:{s:4:"rows";i:5;}s:6:"weight";i:0;s:6:"module";s:4:"text";}s:11:"description";s:0:"";}