This has been debated a lot over the years. We all know SNK had some colorful marketing, "24Bit" right.



The CDZ was marketed in Japan as having a "Double Speed CD-ROM Drive." Were they lying? Let's look at the evidence.

I first took a look a this site with 'X' drive specs:
http://whatis.techtarget.com/definit...sc-access-time

I know these are probably not 100% accurate, but I think its safe to say it's a good baseline. I would also think it's safe to say that a 1x speed cannot read a disc spinning at speeds in the high 2x ranges.

So let's start there, CD speed. I took an unmodified Top Loader and CDZ, marked a disc with some white tape and filmed in slow motion. Here are the results.

This video shows roughly how many rotations within a 1 second time frame.



The Top Loader spins at around 8-9 revolutions per second, or what would be around 480-540 RPM. Easily in the 1X chart above.

The CDZ spins between 17-18 RPS, or 1020-1080 RPM. So double the speed of the Top Loader and within the 2X range on the chart.

The same game was used, Puzzle Bobble, both during data load progress. I just picked those two time frames because the white marker was in a good position to easily read rotations.

OK, so we know the rotation speeds. I took it a bit further. I hooked up the Top Loader CD Drive to my CDZ and it worked. Guess what speed it ran? The same 1x rotation speeds as the Top Loader with no change at all.

Lets look at the chips. The Top Loader uses the LC8915 "CD-ROM host and error correction chip"

https://wiki.neogeodev.org/index.php?title=LC89515

The specs of that exact chip doesn't say anything about "Single Speed", however, its upgrade does. The LC89617:

The last line, "The improved version (of the Top Loader chip) additionally supports double speed operation". So I think it's safe to assume that the older Top Loader chip does not support 2x.

From there I put a CDZ drive in the Top Loader and it does just that, the drive slows down operation to the 1x speeds. That's pretty convincing to me that there are 2 different drive speeds.

When you load a game in a regular CDZ there are 2 speeds that you can see without a camera, high speed when reading data, then back down to low when playing the Redbook CD audio.

I know RPMs are not definitive results, what we need next is a way to measure the actual transfer rates.