AES cartridge
A NEO-ZMC2 or PRO-CT0 chip is used to pre-serialize sprite graphics to be output to the cartridge edge. For the PRO-CT0 carts, a NEO-ZMC chip can also be bankswitch the M1 ROM.
This is the main difference with MVS cartridges and is the reason MVS to AES convertors were made.
The cartridge connector has 2*2*50 (200) pins. See Pinouts#AES_Cartridge.