Complex sentence: EIAJ-2 used a cartridge that contained a supply reel; the take-up reel was part of the recorder, and the tape had to be fully rewound before removing the cartridge, a slow procedure.
Split into simpler sentences: EIAJ-2 used a cartridge that contained a supply reel, but not the take-up reel. As the take-up reel was part of the recorder, the tape had to be fully rewound before removing the cartridge, a slow procedure.