Siri, the first virtual personal assistant, arose from decades of SRI research in artificial intelligence (AI). The technology was developed through the SRI-led Cognitive Assistant that Learns and Organizes (CALO) project within DARPA’s Personalized Assistant that Learns (PAL) program, the largest-known AI project in U.S. History.
Siri is a spin-off from a project developed by the SRI International Artificial Intelligence Center. Its speech recognition engine was provided by Nuance Communications, and it uses advanced machine learning technologies to function. Its original American, British and Australian voice actors recorded their respective voices around 2005, unaware of the recordings' eventual usage. Siri was released as an app for iOS in February 2010. Siri has become an integral part of Apple's products, having been adapted into other hardware devices including newer iPhone models, iPad, iPod Touch, Mac, Air Pods, Apple TV, and Home Pod.
Siri supports a wide range of user commands, including performing phone actions, checking basic information, scheduling events and reminders, handling device settings, searching the Internet, navigating areas, finding information on entertainment, and can engage with iOS-integrated apps. With the release of iOS 10 in 2016, Apple opened up limited third-party access to Siri, including third-party messaging apps, as well as payments, ride-sharing, and Internet calling apps. With the release of iOS 11, Apple updated Siri's voice and added support for follow-up questions, language translation, and additional third-party actions.
Siri's original release on iPhone 4S in 2011 received mixed reviews. It received praise for its voice recognition and contextual knowledge of user information, including calendar appointments, but was criticized for requiring stiff user commands and having a lack of flexibility. It was also criticized for lacking information on certain nearby places, and for its inability to understand certain English accents.

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