16 I am retrieving data from some old optical discs. I came accross a CD with physical hole about 1 mm in diameter in the data layer. The plastic carrier is fine. The hole is actually in a place, where data is stored. But when I have performed a surface scan in ISO Buster and it finished with a success as if nothing was there. The data could be read from the CD as well. I am aware, that the filesystems for optical drives could employ redundancy, but was that optional back then (15+ years ago) or was every disc burned that way... so it actually stored more than 700 MB of raw data? But the more mindblowing part for me was, that the ISO Buster surface scan haven't noticed it. Any idea why? hardwarecd-rom Share Follow asked 2 days ago LukáÅ¡ ŘádekLukáÅ¡ Řádek 26911 silver badge44 bronze badges New contributor LukáÅ¡ Řádek is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct. 13 6 How do you know that there is actually data where the hole is? – tofro Commented 2 days ago 5 While CD do contain a lot of error correction (Yes, even back then), having a real hole that large would need a lot of luck to not stamp out whole blocks. So, are you sure the 'hole' really falls in an occupied data area? After all, CD's aren't formatted all the way like disks are. CDs are more like tapes, only used area is written with a format. Any check will only read those areas, nothing else. They can not check unassigned areas. How much data does it contain? Could you add a picture? Also information about type used? – Raffzahn Commented 2 days ago 13 @tofro haha... now I am just wondering whether I am missing something or you are too young to know how optical discs work 😀... the disk is written from inside out and the process or "burning" the data onto it changes its color a little, so by looking at the CD from the bottom, you can actually tell how much of it is filled with data. – Lukáš Řádek Commented 2 days ago 4 If it's a CD and not a CD-R, then the data is there on the polycarbonate body of the disk. The reflective metal layer might be missing (if that's what you called a hole in data layer), but the reflections off the pits and lands still might produce enough variations in signal for data to be read successfully. – Vlad Commented 2 days ago 4 @LukášŘádek Now I'm feeling very old, because CDs are somewhat "modern" to me :) But thanks for assuming I'm "too young" :) – tofro Commented 2 days ago  |  Show 8 more comments