CDZ
The CDZ was released on December 29, 1995 as the Japanese market replacement for SNK's previous efforts (the "front loader" and the "top loader"). The Neo Geo CD had met with limited success due to it being plagued with slow loading times that could vary from 30 to 60 seconds between loads, depending on the game. Although SNK's American home entertainment division quickly acknowledged that the system simply was incapable to compete with the 3D-able powerhouse systems of the day like Sega's Saturn and Sony's PlayStation, SNK corporate of Japan felt they could continue to maintain profitable sales in the Japanese home market by shortening the previous system's load-times.
Popular speculation suggests that SNK made several changes to the CD hardware to end up with the CDZ, with the most prominent rumor being that they increased the CD-ROM drive speed from 1x to 2x. The truth, however, is that the CDZ had a larger amount of cache. Though the CD-ROM motor in the CDZ may have been more efficient than the one in the original, it was still a 1x speed CD-ROM.
This version of the console has a design flaw that sometimes causes it to overheat after certain periods of time, breaking the console in the process and making it hard to repair. This is a result of a lack of ventilation in the cramped housing of the smaller unit and the inability to dissipate heat generated by the newer drive, which could damage the circuit board.
Read more about this topic: Neo Geo CD