The iPad 2 hit U.S. stores today as its maker, Apple Inc., looks to retain a dominant position in the burgeoning tablet computer market, Reuters reported.

In April 2010, thousands of people lined up to purchase what was at that time a new device in an uncertain market. Apple sold 300,000 iPads on the first day and 500,000 in the first week.

Now, with investors keeping a close eye on the market as Apple’s competitors work to catch up, the Cupertino, Calif.-based company has released a thinner, faster version of its first tablet.

Starting today, the iPad 2 will be available at more than 200 Apple outlets in the United States, as well as in stores of AT&T Inc., Verizon Wireless Inc., Best Buy Co., Target Corp. and Wal-Mart Stores Inc.

More than 50 million tablet computers are expected to be sold this year, and Apple is expected to capture more than 70 percent of the market.