with a Genesis system, attaching through an expansion slot on the side of the main console. It requires its own power supply. A core feature of the Sega CD is the increase in data storage by its games being CD-ROMs; whereas ROM cartridges of the day typically contained 8 to 16 megabits of data, a CD-ROM disc can hold more than 640 megabytes of data, more than 320 times the storage of a Genesis cartridge. This increase in storage allows the Sega CD to play FMV games. In addition to playing its own library of games in CD-ROM format, the Sega CD can also play compact discs and karaoke CD+G discs, and can be used in conjunction with the 32X to play 32-bit games that use both add-ons. The second model, also known as the Sega CD 2, includes a steel joining plate to be screwed into the bottom of the Genesis and an extension spacer to work with the original Genesis model. The main CPU of the Sega CD is a 12.5MHz 16-bit Motorola 68000 processor, which runs 5 MHz faster than the Genesis processor. It contains 1 Mbit of boot ROM, allocated for the CD game BIOS, CD player software, and compatibility with CD+G discs. 6 Mbit of RAM are allocated to data for programs, pictures, and sounds; 128 Kbit to CD-ROM data cache memory; and an additional 64 Kbit are allocated as the backup memory. Additional backup memory in the form of a 1 Mbit Backup RAM Cartridge was also available as a separate purchase, released near the end of the system's life. The graphics chip is a custom ASIC, and can perform similarly to the SNES's Mode 7, but with the ability to handle more objects at the same time. Audio is supplied through the Ricoh RF5C164, and two RCA pin jacks allow the Sega CD to output stereophonic sound separate from the Genesis. Combining stereo sound from a Genesis to either version of the Sega CD requires a cable between the Genesis's headphone jack and an input jack on the back of the CD unit. This is not required for the second model of the Genesis. Sega released an additional accessory to be used with the Sega CD for karaoke, including a microphone input and various sound controls. Models Several models of the Sega CD were released. The original model used a front-loading motorized disc