Notes / Questions about Lead-In Reading

[scsi_wuzzy]

Is it possible that some drives support reading further into the lead-in than others? My understanding is that the lead-in is 150 sectors (2 seconds), but all the Plextor drives I've tested using px_d8 1.0 won't read any sectors lower than -75. However, today I discovered that an old Smart & Friendly brand drive supports scrambled reads (using px_d8) to -127 on my Nights into Dreams (USA) disc.

Specifically, the lowest sector I can read with the PX-716AL is the one with preamble:

Code: Select all

00FFFFFFFFFFFFFFFFFFFF0001807361

But the SAF can fetch:

Code: Select all

00FFFFFFFFFFFFFFFFFFFF0001801961

Are there any discs which need sectors dumped from lower addresses than Plextors can do? If so, it looks like SAF drives might work.

[mock]

My understanding is that the lead-in is 150 sectors (2 seconds)

That's not the lead-in, that's the track 1 pregap. The lead-in comes before that.

[scsi_wuzzy]

That's not the lead-in, that's the track 1 pregap. The lead-in comes before that.

I guess I'm confused then. When we refer to a drive's ability to over-read into lead-in, are we actually talking about pregap? For example, the DAE Features site refers to drives which can over-read into Lead-In, Lead-Out, or Both. Can any drives actually return all the raw, scrambled sectors from the lead-in and lead-out, or are we always talking about gaps? It seems like my Plextor drives won't return the whole lead-in, anyway, because I can't get anywhere near the proper number of sectors prior to the first track. At least, not using px_d8.

Basically what I'm trying to figure out is if it's useful at all that this old SAF drive can read scrambled sectors that no other drives I've tested have been able to read. I think the perfect drive would be able to dump raw, scrambled sectors (with subcodes) all the way from the lead-in to the lead-out, but I'm not sure any drive can actually do that.

Edit: So it looks like Truman's Cdtool can read all the way back to sector #1 on the PX716AL, so I guess the limitation in reading lead-in is just present when using the 0xD8 read command?

And we can read subchannel data from the lead-in, too, which means we can actually just dump raw TOC data from the subchannel, right? Is there some advantage that cuesheets have over raw TOC data dumps from the lead-in subchannel data?

[F1ReB4LL]

When we refer to a drive's ability to over-read into lead-in, are we actually talking about pregap? For example, the DAE Features site refers to drives which can over-read into Lead-In, Lead-Out, or Both. Can any drives actually return all the raw, scrambled sectors from the lead-in and lead-out, or are we always talking about gaps?

Always about gaps, since the drives without that capability can't read anything before sector 0.

Edit: So it looks like Truman's Cdtool can read all the way back to sector #1 on the PX716AL, so I guess the limitation in reading lead-in is just present when using the 0xD8 read command?

There are 2 limitations: audio cds are capped at -75, data cds at around -142...-143. When you use 0xd8, audio cd limitations are used.

For Plextors (PX-708 to PX-760, at least) there is a possibility to read the whole TOC and full first pregap area: you should open cdtool, disable c2 errors reporting and dump either -5000 to 0 range or $FF000000 to 0 range. You should get the TOC dumped multiple times and the first pregap somewhere inside the dump, sometimes there are even data sectors from 0+ range (yes, somewhat random, but you should be able to find all the needed TOC and pregap sectors there).

And we can read subchannel data from the lead-in, too, which means we can actually just dump raw TOC data from the subchannel, right? Is there some advantage that cuesheets have over raw TOC data dumps from the lead-in subchannel data?

Well, there was a standalone branch of Redump.org called "Rawdump.net", which tried to include first pregaps and TOC dumps, but it's dead now. The only real advantage is that the dump is more "complete", if TOC area is there and, theoretically, you can use a 2448/sector data+sub dump with TOC area as a single rom file, with no cue or metadata needed.

I'd say that it's way more problematic to dump the lead-out area, since different drives stop dumping at different addresses and it's hard to determine the very last lead-out sector for the dump. Saturn and Dreamcast are even more problematic due to those rings, which are also dumpable, but different drives are able to dump different amount of sectors.