technut wrote:I see you talking about C1 and C2 errors. I assume this is two out of the three types (or am I way off?). What is the third type of error detection and correction? Is there a good simple explanation of C1 and C2 errors?
At the most basic (and this really oversimplifies and glosses over a lot), the C1 layer corrects the most common errors, the C2 layer corrects "bigger" errors that make it past the C1 layer, and the third layer that is included in mode 1 and mode 2 form 1 discs consists of extra data bytes used for EDC/ECC. It corrects errors that get past the C2 layer. In an audio disc the drive will attempt to mask errors that get past the C2 layer by guessing what the correct value should be. More reading material may be found here:
http://www.roxio.com/en/support/cdr/cderrors.html http://www.cdpage.com/dstuff/BobDana296.html#3 http://www.mscience.com/faq13.html http://www.cdrlabs.com/phpBB/viewtopic. ... 6820#46820 http://www.cdrlabs.com/phpBB/viewtopic.php?t=8194 (a little more specifically,
http://www.cdrlabs.com/phpBB/viewtopic. ... 6820#46820 )
http://club.cdfreaks.com/showthread.php ... adid=61943 technut wrote:When you write to a CDR or CDRW, is it immediately obvious that the information will be readable?
You can test to verify that the disc is good immediately after burning by making use of a variety of programs such as CD Speed, CD Doctor and CDCheck.
technut wrote:Does the writer know that the info will be readable (in other words, does it try to read it back), or is it up to the user to then run a verification program to verify that each file can be read?
You can do either or both. Burning programs such as Nero contain a "verify data" option that reads back the data from the freshly written disc at the end of the burn. You can also compare it yourself to the original data using programs such as CDCheck or MD5summer. All of the programs I have listed here (with the exception of the "verify" option in Nero Burning ROM itself) can be used at any time after a disc is burned, whether that is minutes later or years later.
technut wrote:I suppose it would be a better choice to actually verify that the info written to the new CDR/CDRW actutally MATCHES the source data (which is more than just verifying that SOMETHING can be read). This would involve a program to compare each file on the target to the source.
Again, the verify option, CDCheck and MD5summer, among others, do this. Furthermore, barring a bug in the writing program, a disc that is readable does guarantee that the data matches.
technut wrote:Is it standard practice of people using CDR's or CDRW's to use an app to verify data integrity (checking that each target file actually matches each source file), or is the reliability so good now that once a CD gets burned, you know without question that it is both (a) entirely readable and (b) the data on the CDR/CDRW actually matches the original source?
That depends on each individual and his or her comfort level. I often do, but not always. It depends on how critical the data are.
technut wrote:When you write a CDR or CDRW, is it standard for there always to be these low level errors (later corrected by the error correcting process)? In other words, are CDR's or CDRW's ever (in reality) burned without low level errors, or do they all have them?
Yes, it is inevitable that there will be some errors at the lowest level (C1). As I said in previous posts, the designers of the technology anticipated this and designed in error detection and correction to account for it. Let me ask you, do you trust the pressed CD-ROM discs from which you install your software? The CD-R discs I burn are far better quality with lower error rates than most of the pressed CD-ROM discs I see. By the way, the error detection and correction used on CD-R discs is the same as used on commercial pressed CD-ROM discs.
technut wrote:Is the error correction used reliable enough that, unless scratched or otherwise damaged, the CDR or CDRW can be used as a reliable backup tool?
Yes, yes, yes! Why do you refuse to believe us? And in fact the error correction is reliable enough that even with scratches (assuming they aren't too extensive) the data can be read back with 100% accuracy. Of course, things can go wrong, as with any technology, and some media and drives don't do as good a job as others. But you have been given the tools to protect yourself against this eventuality. You can use the listed software to test your own discs, and you can read these forums to find out what drives and media are better quality. Before you ask again, spend some time thoroughly reading these forums and the various reviews.
technut wrote:Which brings me to my next to final question: would the user know if the error correction did not properly correct a low level error? Or would the user only discover it later when he/she found the data to be corrupt?
If the disc can't be read due to errors, you will get a read error. It won't just quietly sneak by and show up as corrupted data that appeared to read correctly. There is some infinitesimally tiny chance that the errors would just happen to corrupt the data in such a way that the error could not be detected, but that is not a realistic fear.
technut wrote:Finally (yea!
), when writing to a hard disk, if a bad sector is encountered, the drive will mark the sector as bad and not attempt to write to it again. Do CDR's and CDRW's do the same thing?
The question is irrelevant for CD-R discs since they can only be written once. Such mapping is done with packet writing software on CD-RW, depending on the packet writing technology used. However, that is one aspect of recordable technology that I don't recommend. CD-RW media in general is less reliable than CD-R, and packet writing even more so. Some people have great success with it, but others have lost data due to bad packet-writing software or defective CD-RW discs.
cfitz
. I was going to make it separate posts, but I figure since it's all one topic, it's simpler to keep it as a single thread. Many thanks to those who possess the amazing knowledge required to respond!