The iPod may finally have a serious competitor. The company that brought us the Walkman is entering the hard disk music player arena now dominated by its trendsetting-rival Apple.

Sony has unveiled its newest Walkman, a palm-sized, aluminium-encased player that can store up to 13,000 songs on its 20-gigabyte, 1.8cm-diameter hard drive, and promises 30 hours of playback on a rechargeable battery.

Weighing 3.8 grams, the new Sony NW-HD1 is smaller and lighter than the iPod's 15-, 20- and 40-gigabyte models, and just slightly larger than the 4-gigabyte iPod Mini. Sony claims the portable player is the smallest of its class.

The product will be available in mid-August for less than $400 (£220), Sony said.

"I'd call it an iPod challenger and one that will keep Apple on its toes," said Richard Doherty, an industry analyst with the digital media consultancy the Envisioneering Group.

Apple was not the first company to introduce a high-capacity hard-disk portable music player, but its October 2001 launch of the iPod defined the market. The product's runaway success - with an estimated 3m units sold - has since drawn other rivals, including Dell and Samsung.

Still, Apple leads with about a 60% share of the hard-disk drive player segment in the US and about 30% of all portable music players, according to Michael Goodman, an analyst at the Yankee Group market research firm.

Sony's sleek new Walkman is a highly anticipated and belated entry but will likely be Apple's fiercest competitor yet, Mr Doherty predicts.

Portable music is not new to Sony. It pioneered the category when it introduced the original Walkman in 1979. But in the past few years, analysts say, Sony lost some of its lustre as it aggressively pushed mini disc-based music players, and sales - except for in Japan - fell short of expectations.

"Apple's iPod came out, and it was so successful, it really forced Sony's hand," Mr Goodman said.