For example: the CDs we find nowadays on the market are the 640 MB and 650 MB. We will hardly ever find CDs with more or less capacity, principally at accessible prices. When recording this kind of CD, we have a problem: how to do it?
First of all you should understand how data is recorded in CDs. It is recorded in sectors of 2352 bytes. From them, only 2048 are for data. The remaining 304 bytes are used for error correction and other things. Something extremely important to avoid disk read errors that are usually solved with the retry command, mainly if your media has high rates of block read error (BLER).
CDs recorded in this format DATA + CRC + INF are also called Mode 1. It is due to Mode 1 that you can only record 650 MB in a CD physically developed to 740 MB of audio.
A common error in those calculations is to assume that the manufacturer of your CD understands megabyte as the manufacturers of HD, that is, 1000 x 1000. Megabyte for the CD manufacturers is what it really is, that is, 1024 x 1024. It also explains the fact of 680 MB CDs on the Brazilian market. Those CDs are not of 680 MB! They are of 650 MB like any other, the difference is how the megabyte éinterpreted. In the case of those CDs it is exactly like the HD manufacturers do and those CDs are usually made by HD manufacturers, such as Samsung. It is even interesting, because there are CDs by Samsung with 650 MB and 680 MB labels. You may think they are different CDs but they are the same, but one is produced by a unit that also produces HDs and the other not. Summarizing, a 680 million byte CD has 650 MB and not 680 MB.
So, how can a 650 MB CD support up to 740 MB? Simple, just use the space reserved for CRC + INF to also record data, what gives us 80 MB more in a CD. CDs recorded like this are referred to as CDs in Mode 2.
Some software allow us to make this kind of recording, but not all recorders allow us to make it. Some recorders (most of the ones sold in Brazil) are programmed to record the CRC + INF in the disk, no matter the command of the software. It is necessary to be careful with this, because if the software does not know how to deal with this error and correct the size of the generated CD image, you can lose a CD and even damage your recorder. We have not seen any manual that made reference to that kind of characteristic of the recorder yet, and the manuals that inform they record CDs of up to 680 MB are usually making the mistakes described above.
CDs recorded in Mode 2 are not easily read in any CD drive and can show many errors from one computer to another, according to the configuration of internal devices. Before recording a CD in Mode 2 and saving some money with this procedure, you need to consider how much time it can cost you.
When recording CDs in Mode 2 use high recording surface density media, developed to high speed recording drives and record the CD in 1X. All this to prevent errors. It is needed to remember that this kind of recording ends up in reducing the lifetime of the CD, by the number of times the laser beam will go over the same parts searching for information that does not exist and re-reading sectors that became errors.
