Portable MP3 players are still in their infancy. The world may have gone MP3 mad - the hard disks of millions of PCs are filled with them - but only a small percentage of users actually download their software collection for music on the move.

To refresh your memory, MP3 is a method of digitally-encoding music so it takes up far less storage space compared to normal CD files. Typically, an MP3 file of decent quality is twelve times smaller.

The first portable players were about the size of a Walkman-style device. They came with limited memory (usually enough for around 45 minutes of music) and had to be plugged into a PC for tracks to be downloaded.

Since then, the industry has moved quickly. MP3 players today are very different. Many of them don't look like a music device at all.

The trend started with the Maycom Merit. A tiny MP3 portable about the size of a box of Swan Vestas, the Merit also has a built in FM radio, for those moments when the MP3 music has run out.

Originally priced at around £150, the Merit has since been surpassed. Today, it can be picked up for just £50, which makes it a good introduction to portable MP3 players. Be aware, however, that you need to budget for a better pair of earphones. The ones given away with the Merit sound awful.

At least the Merit still looks like a music player (albeit a very small one). Soon we will be foot tapping to tunes on our mobile phones, our pens and even our watches. All this technology is available now and, if you have the money, it can even be purchased over the counter at your local computer store.

First up is the Casio Wrist Audio Player - a fancy name for a chunky watch that also plays music. It's packed with a 16MB multi-media flash card - that's enough for about 15 minutes of CD quality sound. Drop the bit-rate to FM radio quality though and you can cram on around half-an-hour.

It may sound cool but, in practice, the watch is too big and you'll get strange glances when you plug earphones in for some private listening.

Until Casio can reduce the size of its MP3 watches, the Wrist Audio Player will be nothing more than an interesting curiosity.

More impressive is the Sony Music Clip - a small device that looks like a disposable pen and clips to your top pocket in the same way. It offers a more substantial 64MB of storage and connects to a PC via the USB port for rapid downloads.

There is a drawback. Sony doesn't support MP3 - its music division is losing millions to MP3 files illegally distributed via the Net - so it has created a new format called OpenMG. It sounds great but you won't be able to download much via the Internet because everyone else is sticking with MP3.

MP3 players are also finding their way into mobile phones and the next generation of personal digital assistants. Any Pocket PC device will already play MP3 tunes.

Mobile phone players will come into their own when (and if) the third generation telecoms networks take off because they will offer sufficient speed to download tracks direct to a handset.

Real MP3 fanatics may also be interested in the in-car players coming soon.

Currently all the rage in Japan, many of these units won't make it to the UK because they are just too specialised.

If you are interested, surf along to www.carplayer.com and have a look at the MP-Rom. This dream machine plays MP3 music, CDs and even DVD movies. It can be installed in a car (which must be a thief's dream) or connected to your home hi-fi.

Despite the emergence of better recording formats (Microsoft's own Windows Media Audio claims better sound quality and even smaller file sizes) and the demise of the infamous Napster file sharing site, MP3 shows no signs of dying off just yet.

And with first generation players now available for just £50 - less than the cost of a decent personal CD player - the format is within reach of everyone.