Until recently, Web mail meant sending forms back and forth online. Check an item to delete and hit a button. A remote mail server receives instructions and responds with an entirely new page, which is missing only the one deleted item.

Enter Yahoo Inc. and an interface it is testing using technology from an Ajax pioneer it bought, Oddpost. Delete an item this time, and Ajax reconfigures the page immediately without waiting for a response.

Open a message to read, and the browser fetches only the message's body - it already has the subject line and other header information and doesn't have to waste time duplicating that data.

CNN's latest story Web-based software challenges Windows evaluates the threat to Microsoft Office and Microsoft Windows from Ajax, a set of Web development tools that speeds up Web applications by summoning snippets of data as needed instead of pulling entire Web pages over and over.

Ajax applications look almost as if they reside on the user's machine, rather than across the Internet on a server. The reason: pages get updated, not entirely refreshed. Ironically, Microsoft invented Ajax to power Outlook Web Access program.