iPod Touch 1st Gen:

- processor runs at 412MHz (620MHz ARM11 underclocked)
- OpenGL ES 1.1
- 128MB RAM
- NO physical volume buttons
- 8GB, 16GB, or 32GB models

iPod Touch 2nd Gen:

- processor runs at 532MHz (620MHz ARM11 underclocked)
- OpenGL ES 1.1
- 128MB RAM
- Has physical volume buttons
- OS 3.0+ adds Bluetooth support
- 8GB, 16GB, or 32GB models

iPod Touch 3rd Gen:

- processor runs at 600MHz (800MHz ARM Cortex-A8 underclocked)
- OpenGL ES 2.0
- 256MB RAM
- All other features of 2nd Gen.
- Available in 32 or 64GB
- "3rd Gen" 16GB model does NOT have new hardware, it is a rebadged 2nd Gen.