The errors are not required…regular bit patterns are…
There are a number of issues:
The ‘read’ thing: SafeDisc 2 includes ‘weak’ sectors which appear to be errors. They are not really errors, it’s just unusual angularity in the transition from pit to land to pit - it doesn’t really accord with any of the coloured book standards; smart chipsets like those found in Toshibas will skip them really, really quickly; chipsets in Asus CD-ROMs, for example, will choke. The errors are not essential to a working backup (at this point in time!). The errors are there to defeat the read process.
The ‘write’ thing: SafeDisc 2 incorporates “REGULAR bit patterns” in sectors like this: 1010101010101010… and so on in an area on the disc - where doesn’t matter but you’ll find them with a hex editor. Each 1 and 0 and the change from each binary bit is an artefact. To create this pattern on a pressed disc requires small artefacts (the pits & lands including the transition - remember the transition to pit is a 1 and the land is a zero) and greater precision in the die that stamps the blanks. Obviously this is more expensive because of the precision involved. However, including some regular patterns seems to be worthwhile. Why? and how does it work?
EFM encoding: ALL data written to a CD-R/W is EFM encoded (yes it is). Eight bits are taken and modulated (more bits added) to fourteen bits (another three are actually added to the 14…eight to fourteen you see then it’s seventeen really) so that the artefacts (pits, lands & the transition) are NO LESS than 3 bits apart, no more than 11 and are an average of seven apart - this is smart error correction code. CD-RW chipsets are just not normally set up to do anything but this because it’s a standard. The Mediatek chipset can ‘ignore’ the EFM standard (we know this is possible because DVD is eight to sixteen, so anything’s possible) and write the regular bit patterns.
It is the guard module in SD2 that looks for the regular bit patterns and then says “OK - protection module, you can unwrap now and run the game!”. If the regular patterns are missing then it’s a no show.
Macrovision knew that certain chipsets can do the correct non-standard EFM encoding required so they included some Windows API code in the guard module; we now know this as the ATIP check which is also seen in SecuROM NEW.
All MMC compliant AT devices (removeable media) must read the ATIP - this is ALL CD-RW. This CAN also include CD-ROMs & DVD-ROMs but not many.
So this is great protection, attempts to defeat the read and attempts to defeat the write using ‘non-standards’.
ISO images: Bandied around a lot; a true ISO image complies with the MMC standard but most of the time we mean it to be a big file on our HDD. What’s important is that it is written correctly.
So what’s the point? You can create an ‘ISO’ image, change it (crack or patch it), then burn it. Presto. Add files, folders or whatever but burn it properly, in accordance with the standard, Mode 1 or Mode 2 but MMC compliant.
You can’t do this with Daemon’s Tools for example because the image is mounted and treated like a real disc - it can’t be modified, it’s just like a real disc.
Ollie decided to include error correction because it is important that physical errors not make it thru the read. Previously, the errors were uncorrected or merely represented as binary data of sorts to complete the file that the TOC needed to see.
I’m not a patch, crack or blocker sort of guy, 'cos that’s no fun. If I can’t backup something like CD-Cops or some of the unknown CD-Checks then I play my game in an emulator like D-Tools.
There are some good links to EFM stuff in the “Any Topic” board in Clone Clinic.
Hope this helps.