1. Physical level.
- Saturn CDs are modified 74min/650MB media.
- roughly in LBA range 297000..297700 there is featureless transition area separating ring from user data.
it's estimated to be about 34 spiral revolutions (for reference - there is no actual spiral there),
but being variable it can also be twice as wide.
- ring itself lasts up until LBA ~328300, spanning approx. 1460 revolutions
it is pressed in such a way that all revolutions in this area contain the same amount of data - parameter is element length,
in contrast to an ordinary CD, where element length is fixed and so data capacity increases a little with every next revolution:
74min: ~36 additional channel bits per revolution
80min: ~34 ...
90min: ~30 ...
99min: ~27 ...
- rings do differ (even though a little) from CD to CD because of variable area width and logical level differences.
2. Logical level.
- 283649 is defined as last sector for user data, so both: featureless area and ring always end up outside TOC
assuming Lead-Out lasts for 6750 sectors, ther still would be sectors left inbetween user data and featureless area
those sectors are filled the same way Lead-Out is - audio silence in main channel, sub-channel continue as Lead-Out
so one can say that Lead-Out lasts up until transition area.
- ring's main channel data, when unscrambled, reveals Sub-Header: 00 00 28 00 and EDC set to 0
Sub-Header Submode byte 28h translates into:
00101000b -> Data = 1, Form = 1 (Form2)
- when left scrambled, main channel user data form patterns consisting of A8h and 59h bytes.
those bytes yield somewhat opposite pit/land sequences:
59h producing long continuous runs, A8h - frequent changes
- when interleaved those patterns form visible inscription: 59h being background and A8h data,
with each revolution taking up exactly 21 sector.
each sector consist from 98 channel frames and ther's 588 channel bits in each frame,
thus on physical level ther's always 21*98*588=1210104 channel bits in this area per revolution.
- main channel ring data is always the same - it can start or cut out little sooner or later but relevant data itself is the same -
those differences that occur do not affect inscription, it's rather an leading/trailing background-only buffer zone.
- ring's sub-channel data is still continuation of Lead-Out with alternating P-Channel, Control set to 0 as for Audio,
TNO set to AAh and MIN, SEC and FRAC referring to Lead-Out's star, so it's slightly different for every CD.
- sub-channel's offset from main channel in ring area would often coincide with that in user data area
but sometimes it would not.
3. Misc notes.
- would ring be recorded on an ordinary CD, padded out by amount of sectors indicated in MSF (~297700),
it would end up then in area with approx. following initial (constantly increasing) channel bit capacity:
following approx. sector ranges would be mapped to area with channel bit capacity closest to that of the ring (1210104):
74min: 276463..276485 - it's user data area.
80min: 293255..293277 - range between user data and transition area - Lead-Out.
90min: 331628..331650 - unused sectors - slightly after ring
99min: 364785..364807 - unused sectors - well over 74min CD capacity
would it be padded to position at about the same radius as original,
channel bits per revolution towards the end of ring would reach then approx. following value: 1304069
- to pass System ID check and proceed for ring,
it's sufficient to have Mode1 track with identifier '*EGA *EGASATURN ' at user data offset 0 in one of first 15 sectors.
- to disable further ring checks after 1st pass (a la System Disc),
it's enough to have additionaly an valid Maker ID field and Product Number filled with special identifier '*EGASYSTEM'
* = S
grayed out are unverified hypothetical values
if you've read thread on cdfreaks
i have a theory, that most likely i won't be able to verify (so i thought maybe somebody can?)
and i can't register on their forum
is it ok to post it here?