Single BIN file in a BIN/CUE format. Might be identical to the ISO format, but this is unconfirmed. Worth noting that Gens does not handle multiple BIN files very well for Sega CD.
For the CUE file:
MD5: 1DF5554545607554F42784F0B9EEFE81
SHA-1: B454309291378D77A8B12E82A8287BE8F0A0093D