Apple Computer Inc.'s iTunes has become the first online music store to break into the top 10 list of music retailers, a market research firm said.

The Apple service made its debut in the third quarter as number seven, The NPD Group Inc. said this week. ITunes was number 14 during the same period a year ago.

“The ongoing and growing popularity of Apple’s iTunes Music Store now positions the company as a leading music retailer, and continues to legitimize legal digital music retailing,” Russ Crupnick, music and movies industry analyst for NPD, said in a statement.

Apple is expected to increase its market share by the end of the year, because of the growing interest in digital music, an expected increase in iPod demand during the holiday shopping season, and the "stocking-stuffer appeal" of iTunes gift cards, the research group said.

The top 10 list is based on the number of CDs sold. In considering music services, which sell many single songs, the researcher uses an equivalency of 12 tracks per album.

The full list from No. 1 to 10 were Wal-Mart, Best Buy, Target, Amazon.com, FYE, Circuit City, Apple, Tower Records, Sam Goody and Borders.