Sony has unveiled its first hard-disk drive-based digital music player to bear the Walkman name. The device was launched today as the Walkman brand marked its 25th anniversary.

The NW-HD1 features a 20GB hard-disk drive and is, according to the company, the smallest music player at this capacity. It measures 89-x-62.1-x-13.8mm and weighs 110g.

The capacity is half that of Apple's highest capacity iPod, but Sony says its player trumps Apple's in terms of the number of songs it can store: 13,000 on the Walkman versus 10,000 on the iPod.

However, Sony's measurement is based on songs encoded using its ATRAC3 (Adaptive Transform Acoustic Coding for MiniDisc 3) compression system at the relatively low rate of 48Kbps while Apple's measurement is based on the AAC compression system at 128Kbps. At the same bit rate, the Walkman can store around half as many songs as the iPod, which is consistent with it having half the storage capacity.

The Walkman supports only Sony's ATRAC3 compression format, versions of which are used with Sony's MiniDisc players and its recently-launched "Connect" online music store. Music files encoded in other formats, such as MP3, first have to be converted to ATRAC3 before they can be played and software to accomplish this is included. Transcoding typically results in some reduction in quality.

On the front of the player is a 1.5-inch backlit display and the on-screen display language can be switched between Japanese, English, French, German, Italian and Spanish.

The player runs on an internal rechargeable battery and Sony says this will last for up to 30 hours when playing files encoded at the minimum supported bit rate of 48Kbps. This falls to 27 hours when listening to files encoded at 64Kbps. The company did not provide battery life details for other bit rates.

Battery life has been one of the biggest complaints that users have had about the iPod and so it’s no surprise that the Walkman beats Apple's quoted "up to 8 hours."

Sony plans to put the NW-HD1 on sale in Japan on July 10 for ¥53,000 (around £270), in the middle of August in the US for less than $400, and later this year in Europe.

While the device is the first hard-disk drive based model to carry the Walkman name, it's not Sony's first hard-disk drive based media player. The company has already launched four such devices -- three under its own name and one under its Aiwa brand -- in the last nine months as it attempts to make a name for itself in the digital music player market.

One of the most recent to be launched was the Vaio Pocket. It went on sale in Japan in June and features a specification close to that of the new Walkman: the same size hard-disk drive, the same support for ATRAC3 only, and the same price.

What makes the two different is a better tolerance on the part of the Walkman model for use on the move, said David Yang, a spokesman for Sony in Tokyo. The Vaio Pocket can also be used as a portable picture album, which is a feature not present on the Walkman.