Maximun size of a CD

[pepodmc]

Hello everyone.

Im making music packs to use with MSU-MD patches and i want yto know the maximun size and minutes capacity of the Mega CD

Because a disc can have 700 mb and 80 minutes of music, but in mega cd specs it says 500mb and 62 minutes.

[TrekkiesUnite118]

It depends on what kind of CD-R you use, if the disc drive can read more tightly packed tracks, and if there's any security data. For example the Saturn's specs say 650MBs is the max, yet it will happily read discs larger than that. In the Saturn's case that limit is to make sure there's still space for the Security Ring on the disc.

Try it with a larger CD and see if the Sega CD will read it. The worst that can happen is you waste a CD-R.

[Silanda]

The Mega/Sega CD's spec for compliant discs is weirdly conservative. I'm not sure of the reasoning behind it, especially as some of Sega's own games exceed it. The documentation says that it's to "avoid problems", but it doesn't expand on what those problems might be. The documentation lists the area above 540MB as reserved, which makes me wonder if Sega were considering doing something else with that space at one time.

IIRC the Mega CD 2 can read fully recorded 80 minute discs, but it's been years since I tried it so my memory may be defective.

[Blades]

The Sega CD (at least the second model with the JVC drive) will read "oversize" pressed audio CDs without issues.

The Mega/Sega CD's spec for compliant discs is weirdly conservative.

Which document explains this?

[Silanda]

The Sega CD (at least the second model with the JVC drive) will read "oversize" pressed audio CDs without issues.



Which document explains this?

The Mega CD Disc Format specifications. Some of the contents confuse me though; I'm not sure whether I'm being dumb, or whether there are some typos or translation errors.

https://segaretro.org/images/a/a5/Me...ifications.pdf

[Blades]

It just follows CD-ROM conventions of the time. 540MB was the original spec, before it was upgraded to 600+MB with new recording technology.

[turboxray]

I replied on the other thread:

It has to do with the 'pit' density/size made up for the CD rom. It's not actually fixed, but can vary in size. As in, you can have a full edge to edge CDROM could be 62 minutes, but also 70 minutes, 74 minutes, 80 minutes, etc all taking up the same amount of physical realstate on the disc. The more you deviate from the norm, the higher the chance a random CD player won't work correctly (it'll skip or miss) - or more sensitive to bumping/noise/vibration (from my experience, anyway). 62 minutes was probably some safe number for development specs-wise. This was an issue with PCE CD too. So while the system handles 80minute CDs, it's more sensitive than say 70 or 74minute CDs. Matter of fact, Ys I & II went over recommended spec and used the 74minute format. In an interview one the producers said they had to get permission to do that. While not SegaCD, I assume it was probably a similar issue. So why would they choose something like 62 minutes? Well, the laser focal capability degrades over time (due to other electronics that control this). From an engineering perspective, you want the most capable reliability over a period of time (life span). A 62 minute CDROM layout probably maximizes that spec within some reasonable margin. I think you'll be safe with 74 minutes if you're trying to adhere to some retro specs. 80minute if you want bend those rules a bit.

Also: CD audio is 2352 bytes per sector while CD data (mode 1) is 2048bytes per sector (because it needs more error correction bits). This is also why you see the 'size' disparity in ratings/capacity. It depends if you measure it in data sectors or audio sectors (and later, form 1 and form 2 of data sectors).