The iPhone 4S (retroactively stylized with a lowercase 's' as iPhone 4s as of September 2013) is a smartphone that was designed and marketed by Apple Inc. It is the fifth generation of the iPhone, succeeding the iPhone 4 and preceding the iPhone 5. Announced on October 4, 2011 at Apple's Cupertino campus, its media coverage was accompanied by the death of former Apple CEO and co-founder Steve Jobs on the following day. Available for pre-order on October 7, 2011 and coming to mainstream availability in retail stores on October 14, 2011 in the United States, Australia, Canada, the United Kingdom, France, Germany, and Japan, sales peaked over its predecessor with over a million sales in the first twenty-four hours of preorder availability and over four million sales in the first four days of retail availability. Further worldwide rollout, including 22 additional countries on October 28, came over the next several months. This iPhone was named "4S" where "S" stood for Siri (Apple CEO Tim Cook confirmed that during the Q&A session at the D10 conference in May 2012), an iPhone 4S-exclusive intelligent personal assistant that was later included in future generations of mobile Apple products. Retaining the most of the external design of the iPhone 4, the 4S hosted revised hardware specifications, most notably an upgrade to the Apple A5 chipset, and an 8-megapixel camera with 1080p video recording. It debuted with iOS 5, the fifth major version of iOS, Apple's mobile operating system, that introduced features including iCloud, iMessage, Notification Center, Reminders, and Twitter integration. Reception to the iPhone 4S was generally favorable. Reviewers noted Siri, the new camera, and processing speeds as significant advantages over the prior model. It was succeeded by the iPhone 5 as Apple's flagship phone on September 12, 2012. The iPhone 4 remained in production, albeit being sold with reduced storage (from 16/32/64 GB down to 8 GB.) It was officially discontinued on September 9, 2014, following the announcement of the iPhone 6 but is currently supported as of iOS 9. However iPhone 4S is still being sold in some countries at low prices such as Philippines. During the course of its lifetime, the iPhone 4S is the best-selling iPhone ever produced and it is the first (and, by the time, the only) iPhone to support five major versions of iOS: 5, 6, 7, 8, and 9. It is also the last iPhone to have the original 30 pin connector as it was replaced by the lightning connector when the iPhone 5 was released.