Apple's unveiling of the iPhone 4S Tuesday disappointed many who were anticipating an iPhone 5, but Siri, the voice assistant feature, has caught the imagination.

Siri is touted as an intelligent assistant that helps you get things done just by asking. Siri understands the context, allowing you to speak naturally when you ask it questions, Apple says.

Siri is the product of a startup that Apple bought last year, and though it sounds like the kind of voice control system that a lot of other mobile handsets offer, the company says it is a lot more powerful.

Apple dedicated a significant amount of the presentation to showing the extent of Siri's ability to interpret requests and respond. Do I need a raincoat today? incites a robo-female voice to reply: It sure looks like rain today, as Scott Forstall, Apple's mobile software executive, demonstrated.

Siri is also claimed to be smart about using the personal information you let it access. Siri helps you make calls, send text messages or e-mail, schedule meetings and reminders, make notes, search the Internet, find local businesses and get directions. Users can also get answers, find facts and even perform complex calculations just by asking, according to Apple.

The big unveiling of the iPhone 4S on Tuesday was the first time most people learned about Siri, but the voice-assistant software is rooted in many years of technical research.

At the conference, Phil Schiller, Apple's marketing executive, called Siri the coolest feature of the new iPhone 4S, and the company is expected to advertise Siri heavily in its sales pitches.