Complex sentence: The HVC-101 also featured a slightly different case design from the NES-101 in order to remain compatible with the Family Computer Disk System, as the area around the cartridge slot of the HVC-101 is flat rather than convex.
Split into simpler sentences: The HVC-101 also featured a slightly different case design from the NES-101 in order to allow compatibility with the Family Computer Disk System. The area around the cartridge slot of the HVC-101 is flat rather than convex.