E-books are also available from online retailers, who increasingly compete by offering e-books at a low price. In 2013, some online retailers offered e-books for less than $10, and some bookstores offered high-quality paper books at less than $10. Some online retailers also began to offer free e-books. In 2009, the online retailers also began to sell e-books in audio format, as well as e-books for tablet computers and smartphones.
The number of e-readers has also grown; in 2009, there were an estimated 2.3 million e-books in the United States. According to a report by NPD BookScan, the top ten publishers in the United States in 2011 had sold, in total, approximately 593 million e-books. By January 2013, the Amazon Kindle had sold more than 100 million units. By July 2014, the number of Kindle devices had increased to 143 million and the Nook tablets to 25 million.
The number of e-readers on the market has proliferated, and the market for e-books has continued to grow. A study by the Pew Internet and American Life Project reported that in the United States in 2008, 10% of households had an e-reader; that had grown to 15% of households in 2011, and that by 2013, the number of US e-reader owners had increased to over 40%. Among the households with e-reader owners, the e-reader was used to read e-books 73% of the time. By September 2014, the Sony eReader and the Barnes & Noble Nook had a combined market share of more than 50%, which together account for more than half of all e-reader sales. In September 2011, Amazon introduced the Kindle Fire tablet, which was followed by the Kindle Fire HD in September 2012, Kindle Fire HDX in October 2013, and the Kindle Paperwhite in November 2014.
The second course has over 300 pages of PDF tutorial documents in the Hindi language. The courses are available in both the PDF format and in the HTML format to make it easier for the learner to read and for an instructor to use. Both the PDF and HTML versions of the tutorial documents are available for download. The uploaded PDF documents take less than two minutes to download, while the HTML documents take less than 15 minutes to download.
In the early 2000s, e-book publishers began experimenting with e-books that were delivered in a specific format called a portable document format (PDF). An advantage of the PDF format is that it can be converted to other formats, including paper books. PDFs can be viewed with many different types of devices, including those that store documents in the web browser, personal digital assistant (PDA), or handheld device. A result of this conversion is that book enthusiasts no longer need to purchase a dedicated e-book device to read e-books on their computers. EPUB has become the standard format for electronic books in the United States, followed by Adobe Digital Editions and Google Books, and even Sony Reader (which has since left the market).
Many e-book readers now support the use of Adobe Portable Document Format (PDF) documents. PDF documents can be viewed on most e-book readers, and the text can be searched and copied to the clipboard. PDF documents allow the reader to take notes and highlight passages as they read, and they remain readable even when the device is turned off or lost. 827ec27edc