dodecahedron wrote:semi-translucent (if that's the right word?)
I think "translucent" by itself is the correct usage, but I know what you mean.
dodecahedron wrote:i didn't think this second mark was so huge, as you put it, remembering the pictures of messed CDs in the Kprobe thread.
Well, that disc is certainly messed up pretty badly, but the inner area around the hole where the spiral groove starts is clear, and the really big marks with large extent in the direction parallel to the groove (the toughest types of defects) are at the far edge of the disc. It might be that those areas don't show up on the test since the test cuts out before it reaches them. I'm not sure.
I did look up the burst error specifications for CD's, and the CIRC is supposed to be able to correct error bursts up to 3,500 bits (2.4 mm) and compensate for bursts up to 12,000 bits (8.5 mm). So that would agree in general terms with what you did and saw. The 4 mm initial mark resulted in damaged sectors (uncorrectable C2 errors), while the 20 mm second mark completely overwhelmed the drive. Of course, I'm sure that the actual interaction of the drive with your marks is more complicated than this, but what you saw agrees to the first order.
dodecahedron wrote:where is the ATIP/TOC located on the CD? right at the beginning of the spiral?
The TOC is in the lead-in, which for a single session is at the beginning of the disc. The ATIP is spread throughout the disc (it isn't actually pits and lands on the disc but rather a wobble in the spiral groove that encodes, via frequency modulation, information such as the absolute position within the groove (hence A
regroove). The portion that contains the disc identification code that we call the ATIP code is at the beginning of the groove. Thus, lots of important stuff is at the beginning of the disc around the hole, and if you mess up that portion, you can render the entire disc unreadable.