of portable electronic keyboards in the 1980s. These are known as ROM Packs.

Yamaha has made several models with such features with their DX synthesizer in the 1980s, shortly after Casio's ROM Pack cartridges came to market, such as the DX1, DX5 and DX7 and their PSR keyboard lineup in the mid-1990s, namely the PSR-320, PSR-420, PSR-520, PSR-620, PSR-330, PSR-530 and the PSR-6000. These keyboards