Amazon operates 21 fulfillment centers around the globe totaling over 9 million square feet of warehouse space. It sells a wide variety of products including books, clothing, toys, electronics and more. Amazon's massive technology infrastructure is entirely Linux-based, including three of the world's largest Linux databases totaling over 50 terabytes of storage. While Amazon started as an online bookseller, it now also sells products from third-party vendors which account for approximately 25% of its revenue. Amazon aims to be the most customer-centric company where people can find anything they want to purchase online.