In 1998, Rio introduced the Rio PMP300, the second portable consumer MP3 digital audio player. This development made them the first pioneer in portable digital audio in 1998, with a goal of "putting the most effective technology in the hands of the people". The first MP3 portable player was actually developed my SaeHan Information Systems in Seoul, Koreaimported by Eiger Labs, Inc. Its development, the MPMan, measured at 97 mm tall by 70 mm wide, by 16.5 mm thick, while weighing 2 ounces. The MPMan did not become successful, due to the rapid rise of the Rio PMP300, which was developed soon afterward.

With a size of 3.5" x 2.5" x .625" thick, the Rio PMP300 was black with an LCD screen, and a circular pad with control buttons. These controls were used for moving the tracks forward and backward, repeat, random playwith four preset equalizer settings. There were no artist or title information on the screen, but it did display the track number played. This MP3 player supported MP2 and MP3 format audio files. When made, it shipped with 32 Mbytes of internal memory with a SmartMedia slot, where its users could add more memory of one more 32Mbytes card. This $200 device was powered by a single AA battery for eight to twelve hours of playback time.

What Rio was most known for was the paving the way for the development of the MP3 portable player market for the average mainstream. Without the resources to compete with the main portable players, Apple, Philips, and CreativeRio went the route of competing to be the leader in the compact, durable player. When the Recording Industry Association of America filed a lawsuit against them in October 198, claiming the MP3 player violated the 1992 Audio Home Recording Act, the road was wide open when the three judge panel ruled in favor of Diamond Rio's development. Rio is owned by the Japanese firm, D&M Holdings, who in August 2005, said they would discontinue making MP3 players for business reasons, and moving into another direction.

The Rio Forge Sport line flash players sets the tone for the athletic at heart, who like to play hard with the same caliber of music listening. Offering them three different sizes, 128MB, 256MB, and 512MB players, the Forge Sport Players are built with shock absorbing technology, FM tuner, up to 20 hours of battery life, sport clip earphones, and a stopwatch. The use no moving parts, and stays solid while your body is moving along at a speedy run. If you spend a decent amount of time at the gym you've no doubt seen these small players attached to someone's upper arm in a dead sprint.

The Rio Carbon hard drive players, 5GB and 6GB, are as big as Rio goes in reference to disk space, though the size of the player itself can rival the iPod Mini. With a built-in microphone for voice recordings, you can record important messages to yourself in the 20 hours of battery life you have to use on a single charge- which can be done through USB or a power adapter. If you don't have a massive music collection to store or just want to have enough space to hold a particular genre, this player has more than enough space to accomplish the task.
Some Rio problems of concern are the "jog wheel" and center pad, which seem to cause a good amount of grief as they are not built for maximum durability and become fractured or just plain break in a relatively short amount of time. Another problem for the Rio product that seems to be a problem with several different brands of MP3 players, is difficulty with the battery. It does have strong life when charged and ready to use, but when it goes out it is not replaceable, meaning you must purchase a new player. The battery is supposed to last two to three years, but in many cases it faults in a matter of months leaving the user out in the cold.