mobile devices, has many limits, which may vary, depending on the device. However, newer smartphones overcome some of these restrictions. Some problems which may be encountered include: Small screen size – this makes it difficult or impossible to see text and graphics dependent on the standard size of a desktop computer screen. To display more information, smartphone screen sizes have been getting bigger. Lack of windows – on a desktop computer, the ability to open more than one window at a time allows for multi-tasking and easy revert to a previous page. Historically on mobile web, only one page could be displayed at a time, and pages could only be viewed in the sequence they were originally accessed. However, Opera Mini was among the first allowing multiple windows, and browser tabs have become commonplace but few mobile browsers allow overlapping windows on the screen. Navigation – Navigation is a problem for websites not optimized for mobile devices as the content area is large, the screen size is small, and there is no scroll wheel or hover box feature. Lack of JavaScript and cookies – most devices do not support client-side scripting and storage of cookies (smartphones excluded), which are now widely used in most web sites to enhance the user experience, facilitating the validation of data entered by the page visitor, etc. This also results in web analytics tools being unable to uniquely identify visitors using mobile devices. Types of pages accessible – many sites that can be accessed on a desktop cannot on a mobile device. Many devices cannot access pages with a secured connection, Flash, or other similar software, PDFs, or video sites, although as of 2011, this has been changing. Speed – on most mobile devices, the speed of service is slow, sometimes slower than dial-up Internet access. Broken pages – on many devices, a single page as viewed on a desktop is broken into segments, each treated as a separate page. This further slows navigation. Compressed pages – many pages, in their conversion to mobile format, are squeezed into an order different from how they would customarily be viewed on a desktop computer. Size of messages – many devices have limits on the number of characters that can be sent in an email message. Cost – the access and bandwidth charges levied by cellphone networks can be high if there is no flat fee per month.