Скачать или смотреть HTML5 Tutorial (Section 5-Webstorage in HTML5)

HTML5 Tutorial (Section 5-Webstorage in HTML5)

HTML5 introduces two mechanisms, similar to HTTP session cookies, for storing structured data on the client side and to overcome following drawbacks.

-Cookies are included with every HTTP request, thereby slowing down your web application by transmitting the same data.

-Cookies are included with every HTTP request, thereby sending data unencrypted over the internet.

-Cookies are limited to about 4 KB of data . Not enough to store required data.

The two storages are session storage and local storage and they would be used to handle different situations.

The latest versions of pretty much every browser supports HTML5 Storage including Internet Explorer.
Session Storage:

The Session Storage is designed for scenarios where the user is carrying out a single transaction, but could be carrying out multiple transactions in different windows at the same time.
Example:

For example, if a user buying plane tickets in two different windows, using the same site. If the site used cookies to keep track of which ticket the user was buying, then as the user clicked from page to page in both windows, the ticket currently being purchased would "leak" from one window to the other, potentially causing the user to buy two tickets for the same flight without really noticing.

HTML5 introduces the sessionStorage attribute which would be used by the sites to add data to the session storage, and it will be accessible to any page from the same site opened in that window ie session and as soon as you close the window, session would be lost.