NW-MS90D

The NW-MS90D was a third-generation Memory Stick Walkman that combined built-in flash memory with Memory Stick Duo expansion. It offered 512 MB of internal storage and supported ATRAC, ATRAC3, and ATRAC3plus playback through a backlit LCD. Gapless playback, Virtual Mobile Engine, and canal-type headphones were included, and the model built directly on the NW-MS70D's integrated-flash approach.

The higher capacity made Sony's hybrid Memory Stick idea feel more complete. Earlier Memory Stick Walkmans treated the removable card as the center of the product. The NW-MS90D paired internal flash with Duo expansion, so it behaved more like a self-contained player that happened to allow extra storage.

Gapless playback, stronger battery life, and a more mature compact design gave it a cleaner purpose than the earliest Memory Stick models. It was the high point of that branch before Sony's digital Walkman line settled more firmly around integrated flash players.