It's the Secondary Master in my system. The drive is a 20GB QUANTUM FIREBALL. It's not super new, and I see what you're saying, but this isn't a 2GB relic from the Pentium II days. This drive should not be struggling with .mp3 playback. Background apps have nothing to do with this problem, and Windows did not find any errors on the drive. Again, I don't see how RAM would be an issue if the same files play back fine from the other drive. I'll get around to formatting the drive eventually, but my other drive doesn't have enough space for all 20GB, so it won't be anytime soon.
