The official cause of death for beloved Apple co-founder Steve Jobs was made public on Monday as a private memorial was planned at the company's Silicon Valley headquarters for employees. Local public health officials reportedly determined that Jobs was at home in the Northern California city of Palo Alto on October 5 when he stopped breathing, an underlying cause listed as a cancerous tumor in his pancreas. No autopsy was conducted and Jobs was buried on Friday in a local, non-denominational cemetery, according to documents cited online. His occupation was listed in coroner's paperwork as "entrepreneur." Jobs died at the age of 56 after battling cancer for several years. Word also spread on Monday that Apple planned a tribute to Jobs on October 19 at a private event to be held at an outdoor amphitheater at the company's headquarters in Cupertino, California. "We are planning a celebration of Steve's extraordinary life for Apple employees that will take place soon," Apple chief executive Tim Cook said in a statement released the day Jobs died. Apple has not indicated plans for a public memorial for Jobs, but people have paid tribute to him with flowers, candles, messages and more outside his home, the company headquarters, and Apple retail stores around the world. An Internet movement for an unsanctioned "Steve Jobs Day" on October 14 was building on the Internet and has been augmented by a budding campaign encouraging people to wear black in his honor. Jobs was known for his trademark outfit of black turtleneck shirt, blue jeans, and sneakers. Apple said that pre-orders of the new model of its hit iPhone 4 topped one million units in the 24 hours after the commenced on Friday. Worldwide advance orders for the iPhone 4S, said to be much faster than its predecessor and with improved video and photo capabilities, set a record for an Apple product. "The first day pre-orders for iPhone 4S have been the most for any new product that Apple has ever launched," said Philip Schiller, Apple senior vice president, in a statement. The smart phone, which will sell for between $199 and $399, depending on memory capacity, will be available in Apple stores in the United States from October 14. It will be available in 22 other countries, including much of Europe, by the end of October. The 4S was launched on October 4, one day before Jobs died. His health failing, Jobs had stepped down as chief executive in August and was replaced by Cook, who presided over the launch of the new iPhone.