The featherweight MP3 player you take out jogging will not keep you amused on, say, the 17-hour trip from Atlanta to Japan. Sometimes one or two hours of music is just not enough. That's why hard-drive-based portable music players have become an attractive option. Take the Toshiba MEG50AS Mobilphile™. Its lithium ion battery can play for about 18 hours per charge — and its 5-gigabyte hard drive can hold dozens of albums.

Though not the tiniest portable out there, the Mobilphile player fits easily in your hand.

Yet the player is no larger than a deck of cards, fits handily in a shirt pocket, and weighs about a half-pound with battery and removable hard drive installed. Now doesn't that make a whole lot more sense than carrying a portable CD player and an unwieldy bunch of discs? After all, the songs recorded on those CDs are just bits, and when you compress and transfer them to a portable hard drive like Toshiba's, they become lighter than air.

In look and feel the Mobilphile compares well with Apple's popular iPod. It comes in silvery-aluminum with a blue backlit liquid crystal display measuring 1-3/16 by 1-7/16 inches. A four-way rocker switch shares the front panel with three buttons: play/pause, player menu, and a navigation button that switches between folder display and individual track display. Two large round volume up/down buttons are on the right side. The unit comes with earbuds and a wired remote control with basic transport and volume functions. They are separate, so you can plug them together in series, use the earbuds alone, or use the wired remote with the mini-plug-equipped headphones of your choice.

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The MEG50AS portable comes with a sturdy, rubberized blue case for holding the removable hard drive when it's not in the player.

There are two ways to get music from your PC into the player. One is to use the USB jack. It supports both USB 2.0 and the older, slower USB 1.1. Even at USB 1.1's pokey 12 megabits per second I found it took no more than half a minute to transfer an album's worth of MP3 files from my 2000-vintage Compaq Presario to the Toshiba. The alternative is to plug the removable hard drive directly into your laptop's PC card slot.

One thing you cannot do is bypass the supplied Audio Manager Software. I tried using Windows Explorer to copy MP3s from my PC's hard drive to the Toshiba, and the folders did appear in the player menu, but when I tried to play music the player refused with a "no file found" message. However, after installing the Audio Manager Software — which is similar to Windows Explorer in both look and operation — I quickly moved the same files and played them without a hitch. Supported file formats include MP3, WMA (Windows Media Audio), and WAV (uncompressed).

The Audio Manager Software encrypts all material transferred into the player so that it can't be transferred back out. Various anti-copy systems encoded into certain CD releases and MP3 downloads are supported. For example, if an MP3 file contains a flag saying it can't go beyond the PC, the player won't accept it. Otherwise, anything you can successfully download or rip — with the bundled MusicMatch or the MP3 encoder of your choice — should work fine.

The removable hard drive slips right out of the bottom of the player and fits in a PC card slot.

What about the sound? I put aside Toshiba's merely adequate earbuds and plugged in my whole collection of high-performance headphones. The player sounded very good with the Bose TriPort, Grado SR60, and Yamaha RH-5Ma with volume about three-quarters of the way up. The AKG K240 — a large and inefficient studio-reference model that I use as a torture test — required the unit's full volume capability. The tone controls include a sizzle-and-boom loudness control and two levels of bass boost, but even at the flat setting, the tonal balance was reliable, and the preamp circuitry didn't add any noticeable edginess or noise to what was already in the signal.

At a price of $249.99, the Toshiba MEG50AS Mobilphile isn't the cheapest player around. But that 5GB hard drive will store enough music to entertain you for days at a time. The sound — within the inherent limits of compressed audio — is competitive with the best MP3 devices. And just one look at the sleek package may be enough to make the credit card levitate right out of your wallet.