Key Physical Differences:
2nd Gen vs. 1st Gen
Both 1st and 2nd gen were produced in 8, 16, and 32GB models.
-Chrome border on the 2nd Gen wraps around to the front of item and is visible when iPod is set down flat.
-Black Wifi antenna on the 2nd Gen back is more rounded when compared to the 1st gen.
-Edges on 2nd gen are more rounded than 1st gen.
3rd Gen- produced in 8, 16, and 32, and 64GB
No physical difference between this and the 2nd gen. If the Touch is a 64GB, you know it has to be a 3rd gen. Other than that, the only way to tell would be the serial number.

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