Sega Master System / Mark III / Game Gear
Broadly, the former is found in Master System consoles and the latter in Master System II consoles. However, the opposite is found in a small number of cases. Nevertheless, the terms "SMS1" and "SMS2" are commonly used to distinguish between the 315-5124 and 315-5246 VDPs because the terms are more memorable.
The primary known differences between them are that the SMS1 VDP allows some of the legacy register bits from TMS9918 modes to affect the VRAM addresses generated, as described in the VDP Registers page; and the SMS2 VDP supports the extra-height 224- and 240-line modes.