Sony NW-WM1A Help Manual page 24

Note
On the Walkman, you cannot exchange data between the Walkman memory and a microSD card.
If the Walkman does not recognize the microSD card, remove and reinsert the microSD card into the Walkman.
Do not insert any object other than a microSD card into the microSD card slot.
If the inserted microSD card contains a large amount of data, it may take about 10 minutes or longer for the Walkman to update
the database.
When you remove the microSD card, the following information will be deleted.
The content that is currently being played.
The playback position.
Tracks and the playback order on the play queue screen
Bookmark information for tracks on the microSD card.
Formatting a microSD card will delete all data stored on the microSD card. Save a back up copy of important data.
The contents of the Help Guide may be subject to change without notice due to updates to the product's specifications.
Related Topic
Notes on microSD cards
Formatting a microSD card
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