Joomla admin side access restrictions

Step : 1 

//Prepare the user restriction code

$userlogin =& JFactory::getUser();
foreach($userlogin as $key=>$value)
{
  if($key=="gid")
  {
  $gid=$value;
//Get the current login user Group id
  }
}


//Add the components folder name you want to restrict in below array
$components=array(com_users, com_content, com_modules, com_installer);

//25 is User Group id. Restriction apply to this User Group.
if(addslashes(in_array($_REQUEST[option],$components) && $gid=="25" )
{
  $mainframe->redirect( 'index.php');
}

Step : 2

Place the above code before "echo"  in [ joomla/administrator/index.php ]