The Sega CD was also capable of playing CD+G
discs, which I'm told are karaoke
(after a horrible experience at a party
involving Two Princes
being karaoked constantly I have since given them a wide berth
In a nice touch, game saves were done using the internal memory, of which there were 125 blocks. Most games would take only 4 or 5 blocks, but some (notably Third World War) would require a LOT more. Sega seemed to realize this too late, and added an option for a back-up ram cartridge which could be inserted into the cartridge slot on the attached Genesis. This didn't actually go on sale for a very long time, but when it did become available you had to once again question what exactly went on in the heads of Sega, as the ram cart had 2048 blocks.
(little sidenote: bit of trivia here, but back in the bad old days of CD-ROM addons for systems, often the cartridge slot was intended to house the system cartridge, which contained the operating system for the CD drive. The SNES CD was going to have this, the TurboGrafx-16 did, but the Sega CD's system was built in.)
As Kit-Lo said there were two versions of the Sega CD. The first was designed to fit under the original Genesis model, and had the motor driven door. The Genesis II could also fit on it, but its smaller width left an ugly gap. Meanwhile, attaching the original Genesis to the Sega CD II would result in an overhanging bit, for which Sega thoughtfully included a thingy to attach to the base. I still have this somewhere.
There was a third version of the Sega CD, which was basically Sega's answer to TTi's Turbo Duo. Called the WonderMega or X'Eye, this was made by JVC and was basically was the Genesis and Sega CD in one convenient unit. Sega also made a portable version called the Sega CDX which was basically a huge portable CD player that could also play Genesis and Sega CD games. The 32X was reportedly compatible with the X'Eye but the instruction manual had a small note included countering the instructions on mounting a 32X on a CDX saying they in fact were NOT compatible.
fondue says only four people in the world owned the Genesis/Sega CD/32X 'supersystem' (I was one of them) so I'd like to speculate that only one person ever cried and beat the walls over not being able to plug a 32X into their CDX and play hi-res Slam City with Scottie Pippin.
My personal recommendations of games for the system include:
-Snatcher, an excellent Blade Runner homage which is part of the Policenauts series by everyone's favourite author of endless codec conversations, Hideo Kojima.
-Third World War, a marvellous strategy game combining turn-based global strategy and number crunching with Powermonger-style real time strategy.
-Wing Commander, a spectacular version of the PC classic, with full speech and orchestral music.
-The Terminator, massively improved over the Genesis original, this features only a bit of FMV and instead uses the CD to provide huge detailed levels, rotoscoped animation and a rockin' soundtrack by Tommy Tallarico.
-Silpheed, loosely based on the Game Arts original, this is a showpiece title that is also quite excellent fun.
-AH-3 Thunderstrike, by Core Design, this won best game on the system on year, for its huge number of exciting, entertaining first-person helicopter missions.
-Sonic CD, the only Sonic the Hedgehog game I ever bothered completing 'properly'.
In closing, the Sega CD only added one real technical advantage to the Genesis - Mode 7. Nobody cared.