The Sega CD, also known as the Mega-CD in Europe and Japan, was a CD-based add-on for the Sega Genesis. As its name would suggest, it allowed the Genesis to take advantage of the higher-capacity CD-ROM storage medium, enabling features such as Full Motion Video and Red Book CD sound. Unfortunately, the Genesis'/Mega Drive's own processing power wasn't quite enough to take advantage of these features to the fullest. It was released in 1991 in Japan, with North America getting it in 1992 and Europe in 1993. The launch price was $299 (£270 in Great Britain), twice of that of the Genesis itself after it was given a price cut in 1991.
The Sega CD came about because Sega heard rumors of Nintendo's deal with Sony to develop their own CD add-on, and also because NEC had just released a CD attachment for their PC Engine console (ironically, the SNES CD-ROM wound up becoming an albatross and never saw release; Sega wasted no time in mocking Nintendo for this in their ads for the Sega CD). Sega jumped the gun and pushed out their own attachment as a countermeasure: it allowed the Genesis to perform otherwise-impossible tricks similar to the SNES, such as Mode 7 effects and sprite rotation.
The add-on is probably best known for its association with Full-Motion Video games. While not the first or even last machine to host FMV games, they were prominently featured in Sega's aggressive marketing and fairly common for the add-on thanks to Digital Pictures, a major proponent of the game genre. The Sega CD also hosted Digital Pictures' Night Trap, which was immortalized by being featured at a U.S. Senate hearing concerning portrayals of violence in video games. Hosting live action footage on a home console was impressive for the time, but it was heavily degraded by the Genesis's palette limitations and the visuals have aged poorly. (The few CD games that also supported the 32X add-on don't suffer from this issue and fared much better.) To quote Digital Pictures co-founder Ken Melville, "[footage was reduced to] the most horrifying, blurry, reduced-color-palette mess imaginable." The FMV games themselves also quickly gained a reputation for being shallow experiences not worth buying, which contributed to turning people away from the CD.
The Sega CD also received a number of enhanced ports of Genesis games, though many didn't have substantial changes outside of improved soundtracks and a bit of extra content. Despite ending up with a sizable library, the add-on was criticized for being improperly supported between the poorly-received FMV games and the ports that didn't justify the high asking price. While completely original, non-FMV, and actually good games do exist for the Sega CD, they're very few in number and are often overshadowed by the library's poor reputation, with recognition of them being limited to hardcore Sega fans and fans of their respective franchises. The only Sega CD game to break into mainstream consciousness as "good" is Sonic the Hedgehog CD, if only because of the sheer weight of Sonic's brand recognition.
In addition to its tepid audience response, the Sega CD is also seen as a commercial failure, only selling 2.4 million units. (Compare the 30 million Sega Genesis units sold.) While not as disastrous as the later 32X add-on, the lacking reception and sales were the first signs of Sega's eventual decline during the mid- and late-90s that would lead to them leaving the console market. The combination of this and the PC Engine CD's poor sales outside of Japan (as the TurboGrafx-CD) are also credited as a likely factor in Nintendo choosing to stick with cartridges for the Nintendo 64 — right when CD-ROM technology became more readily practical for game developers. Oops.
Today, the Sega CD is generally understood as having had a lot of potential that was sadly never utilized by most developers, with its main stumbling blocks being the Loads and Loads of Loading, poor marketing, high launch price, and the fact that it required both a plug into the Genesis and an independent power adapter. It's seen as a decent addition to any Retro Gaming collection due to its unique software and enhanced Genesis ports, though many of the rarer games have become extremely valuable and thus expensive to purchase secondhand.
- The sprite capabilities are identical to the Genesis/Mega Drive console, but the CD can do sprite scaling and Mode 7 effects.
- Like the main console, the CD add-on has limited support for real time 3D, such as the main fighter and enemies in Silpheed (with the backgrounds being pre-rendered full-motion videos), Stellar Fire and the port of Starblade.
- A Motorola 68000 chip running at 12.5 MHz. The 68000 chip already in the Genesis becomes the sound chips's CPU.
- 512 KB of main RAM and 256 KB of video RAM.
- 64 KB of sound RAM.
- 16 KB of CD drive cache.
- 8 KB of back up RAM, with memory cartridges going at 128 KB.
- Same as the Genesis/Mega Drive, but has a extra chip that can do scaling and rotation effects like the SNES's Mode-7 chip (the SNES has 2 PPUs, 1 for modes 0 to 6, and the other for mode 7) with the DPS1 chip and playing FMV video.
- Because of the additional memory of the discs, Sega CD/Mega-CD games can play pre-recorded CD quality music for the main games. The drive also doubles as a standard CD player. Discs are multi-partitioned, with track 1 carrying game data and track 2 onwards carrying Red Book CD audio.
- Ricoh RF5C164 note 16-bit 8 channel PCM chip running at 32 KHz (44.1 KHz for CD-DA), also its own CPU running at 12 MHz.
- On Model 2s, the console can receive audio from the CD add-on internally and output the audio mixed. However, on Model 1 machines, a passthrough cable must be hooked into the console's headphones jack to connect it with the add-on, and audio from then must henceforth be received from the add-on instead of the console. As a result, while the Model 1 can be installed on the Sega CD/Mega-CD 2 with a base extension, the Model 2 is incompatible with the Sega CD/Mega-CD 1.
- The Adventures of Willy Beamish
- After Armageddon Gaiden
- After Burner III
- The Amazing Spider-Man vs. The Kingpin
- Android Assault: The Revenge of Bari-Arm
- Brutal: Paws of Fury
- Chuck Rock
- Chuck Rock II: Son of Chuck
- BC Racers (later ported to the 32X)
- Cobra Command
- Corpse Killer
- Cosmic Fantasy Stories (Japan-only)
- Cyborg 009
- Dark Wizard
- Demolition Man
- Double Switch
- Dracula Unleashed
- Dragon's Lair
- Dungeon Explorer
- Earnest Evans (a Japan-only game which would later be ported to the U.S. Genesis, albeit in a stripped-down state.)
- Annet Futatabi
- Earthworm Jim: Special Edition
- Ecco the Dolphin
- Ecco: The Tides of Time
- Eternal Champions: Challenge from the Dark Side
- Fatal Fury Special
- Final Fight CD (unlike the SNES port, this version had all three characters without the need of having a re-release with Guy in it. Also includes the 2-Player Mode and Industrial Area stage, with the latter featuring Rolento as the boss.)
- Ground Zero: Texas
- Heart of the Alien
- Jurassic Park (Sega CD)
- Keio Flying Squadron
- Kids on Site
- The Laughing Salesman (consists of three episodes from the show in a "Pick your own outcome" style gameplay)
- Lords of Thunder
- Mad Dog McCree
- Make My Video series
- Mansion of Hidden Souls
- The Masked Rider: Kamen Rider ZO
- Mickey Mania: The Timeless Adventures of Mickey Mouse
- Mighty Morphin' Power Rangers (consists of clips from the show with Press X to Not Die slapped all over them)
- The Misadventures of Flink (known simply as Flink for the U.S. release)
- Mortal Kombat CD
- Night Striker
- Night Trap
- Ninja Hayate
- The Ninja Warriors
- Penn and Teller's Smoke and Mirrors (never been released, but had actually been finished and did get in the hands of game reviewers up until the publisher to the game went bankrupt; best known for the intentionally horrendous Desert Bus minigame)
- Popful Mail
- Radical Rex
- Revenge of the Ninja
- Revengers of Vengeance
- Rise of the Dragon
- Road Avenger (a.k.a. Road Blaster FX in Japan)
- Robo Aleste
- Samurai Shodown
- Sengoku Densyo
- Sewer Shark
- Sherlock Holmes: Consulting Detective
- Shining Force CD (a port of the two Shining Force Game Gear games but with better graphics and extra quests)
- Shin Megami Tensei I
- Snatcher (notable in that it was the only English version of the game; in fact, the game was Remade for the Export specifically for North America and Europe without a Japanese Mega CD release because the PC Engine was eating the Genesis' dust in those territories.)
- Sol-Feace (later released as Sol-Deace for the Genesis, the port itself being an exclusive title in the United States.)
- Sonic the Hedgehog CD (the add-on's killer app and the only game which sold quite high and excellently)
- Space Ace
- The Space Adventure (based on the Space Adventure Cobra manga)
- Star Wars:
- Star Wars Chess
- Star Wars: Rebel Assault
- Surgical Strike
- Time Gal
- The Terminator
- Wild Woody
- Wonder Dog