A mobile browser is a web browser designed for use on a mobile device such as a mobile phone or PDA. Mobile browsers are optimized so as to display Web content most effectively for small screens on portable devices. Mobile browser software must be small and efficient to accommodate the low memory capacity and low-bandwidth of wireless handheld devices. Typically they were stripped-down web browsers, but some more modern mobile browsers can handle more recent technologies like CSS 2.1, JavaScript, and Ajax.