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Thread: Neo Geo CDZ Single or Double Speed: Let's Discuss

  1. #1
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    Steers&Queers Neo Geo CDZ Single or Double Speed: Let's Discuss

    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.

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    Kyokugen's Student
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    What are the chances it spins double speed, but doesn't get the higher transfer rate? What would even be the point of the (probably more expensive) double speed drive then?

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    Quote Originally Posted by fenikso View Post
    What are the chances it spins double speed, but doesn't get the higher transfer rate? What would even be the point of the (probably more expensive) double speed drive then?
    I'm assuming that the CDZ isn't getting the full benefit of the 2x speed, but there is some improvement.

    The CDZ's loading improvements aren't solely connected to some "faster caching etc", because if it was, I'd think we would see some boost when hooking up the Top Loader drive to the CDZ. Again, the load times were identical to the Top Loader when I put a Top Loader CD Drive on the CDZ.

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    Thanks for going to the effort of looking into this properly - as a big NGCD fan I certainly appreciate it

    The CD-ROM on the CDZ is from Sharp, and is a different model to the one used in the earlier machines, but that could be just down to obsolescence, or cost reductions. Is there any way of running the part number for the CD-ROM past Sharp to confirm the spec? I've done searches online, but can only find links into parts suppliers with info that generally infers that this CD-ROM was also used in CD players of the time.

    If the latter is true, why put a dual speed CD drive in a CD player? To keep costs down you'd just use a single speed drive, no?

    I really don't know enough about the CD format... : /
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    Quote Originally Posted by NeoTurfMasta View Post
    I'm assuming that the CDZ isn't getting the full benefit of the 2x speed, but there is some improvement.

    The CDZ's loading improvements aren't solely connected to some "faster caching etc", because if it was, I'd think we would see some boost when hooking up the Top Loader drive to the CDZ. Again, the load times were identical to the Top Loader when I put a Top Loader CD Drive on the CDZ.
    Great tests and an awesome observation. I know the CDZ drive speed has been contested over the years, but this finally sheds more light on the CDZ's loading speed solution. Thank you as always NTM!

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