paper, a technology which allows a display screen to reflect light like ordinary paper without the need for a backlight. Among the first commercial e-readers were Sony's Data Discman (which was using Mini CDs with special caddies) and the Rocket eBook. Several others were introduced around 1998, but did not gain widespread acceptance. Electronic paper was incorporated first into the Sony Librie that was released in 2004 and Sony Reader in 2006, followed by the Amazon Kindle, a device which, upon its release in 2007, sold out within five and a half hours. The Kindle includes access to the Kindle Store for e-book sales and delivery. , new marketing models for e-books were being developed and a new generation of reading hardware was produced. E-books (as opposed to e-readers) had yet to achieve global distribution. In the United States, as of September 2009, the Amazon Kindle model and Sony's PRS-500 were the dominant e-reading devices. By March 2010, some reported that the Barnes & Noble Nook may have been selling more units than the Kindle in the US. The Ectaco jetBook Color was the first color e-reader on the market, but its muted colors were criticized. As of 2021, a few color E-ink readers have been introduced into the market. Research released in March 2011 indicated that e-books and e-readers were more popular with the older generation than the younger generation in the UK. The survey, carried out by Silver Poll, found that around 6% of people over 55 owned an e-reader, compared with just 5% of 18- to 24-year-olds. According to an IDC study from March 2011, sales for all e-readers worldwide rose to 12.8 million in 2010; 48% of them were Amazon Kindles, followed by Barnes & Noble Nooks, Pandigital, and Sony Readers (about 800,000 units for 2010). On January 27, 2010 Apple Inc. launched a multi-function tablet computer called the iPad and announced agreements with five of the six largest publishers that would allow Apple to distribute e-books. The iPad includes a built-in app for e-book reading called iBooks and had the iBookstore for content sales and delivery. The iPad, the first commercially profitable tablet, was followed in 2011 by the release of the first Android-based tablets as well as LCD tablet versions of the Nook and Kindle. Unlike previous dedicated e-readers, tablet computers are multi-functional, utilize LCD touchscreen displays, and are more agnostic to e-book vendor