The expansion port is no slower than the cartridge port though: that's not the problem. The big bottleneck for graphics is the Genesis VDP itsself with DMA limitations: same things apply to all genesis games (including virtua racing -hence the screen clipping and limited framerate -though there's also a limit on rendering speed independent of the DMA and VRAM limits).
The 32x bypasses all of that by having separate video, which is often suggested as what should have been done with the CD. (as a top mounted unit and requiring a video mixing cable)
Had the Genesis had dual VRAM banks the limitation would be substancially reduced, though the color limits wouldn't change. (one hypothetical suggestion was to have VRAM selectable as 2x 32 kB banks OR 1x 64 kB bank as it is now -rather than doubling RAM and adding more to cost)
The RAM limitations aren't so bad, but games would need to be designed catering to such a system, different limitations than carts, trade-offs. Straight cart game ports would only work for 256 kB (2 Mbits) or less, past that you need bank switching, and past 768 kB (6 Mbits) you need multiple loads. Mortal Kombat would be the last example, but it also seems like a fiarly bare bones port: they technically could probably have added more animation and almost definitely improved sound samples. (or more sound samples at least -the sample playback isn't too bad compared to some genesis games) Again, you're limited to 64 kB of sound RAM, but you could reload that from main memory if necessary. (but not from CD in-game, too slow, so only reloading that between stages)
The Sega CD is still a lot less limited in any respect than NEC's PC Engine CD, or even the expanded Super CD. The original CD has only 64 kB of program memory (another 64 kB dedicated to the ADPCM chip). The Super CD increased that to 256 kB the same year the Mega CD was released (1991), so still far more limited. (hence why Street Fighter II came out on hucard)
They eventually released the arcade card with 2 MB, but that was a bit late and only a couple games used it iirc. There's also no CD cache in the PCE CD, unlike the MCD.
Ironically, the PC Engine has a comprehensive expansion bus, more than the Genesis cart port has, and had the MD had such most or all of its limitations could have been circumvented (full address range, video and audio mixing through the expansion port, etc -I think even a VDP bus -in the MD's case there's an unused VDP pixel bus which could have come in handy), NEC could have even released the Supergrafx as an add-on with that, but they didn't and used a far simpler CD add-on. (not even adding the supergrafx enhancements to the duo consoles)
Had Sega used the cartridge port for the CD, they could have flat mapped the full 768 kB to main CPU address space, in fact there's a bunch of reserved address space on the cart port. (iirc there's 10 MB total addressed to the cart port, 4 MB used for games and another 2 and 4 MB blocks iirc -I think the 32x used one of those address ranges -as the Sega CD could have in theory)
Otoh, had the expansion port simply been a clone, or near clone fo the cart pinout with similar addressing and singnals on it, that could have been fine too. (and meant the CD wouldn't have to sit on top to benefit. (addign a few more signals like the analog video lines and/or the pixel bus could have been even more useful -and again, similar to the PCE)
Plus the Sega CD still has 256 kB more than the 32x... (and double the program ram -with the word ram configured for ASIC rendering -it's very in configuration similar to the 32x framebuffers -same 80 ns 64x16 kbit FPMDRAM chips actually, the 32x communicates to the MD though the framebuffers too iirc, rather like the word ram)
I'm ranting again though and rehashing some things I've mentioned before.
Yep, but if you go to the Sega CD the you've got:
Silpheed (impressive for the music particularly -also the FMV is a higher framerate than uncompressed video could be, but shows no compression artifacting -granted it would only need ~2:1 comoression, possibly less).
Novastorm for similar reasons to silpheed. (music at least, though the graphics are a bit too posterized to really pick out compression, no microblocking though -the PC version has it and cutscenes using "cinepak for sega" do too; not too much dithering either, just tons of posterization)
Core's games: Soul Star, BC Racers, BattleCorps, AH-3 Thunderstrike (Thunderhawk)
Clockwork Tortoise's contributions of Batman Returns, Batman and Robbin (nice FMV too -they also did the Genesis Game), and Joe Montana NFL Football. -Imagine if Road Rash had been done like the Batman games. (not to mention all the Sega arcade scalers -including the couple on the 32x)
F-1 Beyond the Limit is the only Japanese game to make significant use of the ASIC. (Sonic CD does a bit, bit not especially well)
I'm sure I'm forgetting some others though.


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