Disc spanning is a function used with compact disc (CD) and digital video disc (DVD) burning in which files are separated to automatically fill two or more media. If there is a file that is too large to fit on one medium, then disc spanning will split the file so it can be burned over several media. While this feature is common and may come pre-installed on many operating systems (OSs) and their native burning programs, it is not included on every burning program. This feature is intended as a convenience for users, who otherwise would have to split files manually.
When someone is burning files to an external storage medium, the medium sometimes does not have enough room to fit all the files. This means two or more media must be used, and disc spanning makes it easier to burn to multiple media. It splits the files into groups and each group is burned to a medium. The groups often are made to be as large as possible so fewer media are needed overall.
Files to be burned often are small, meaning several can fit on a single external medium. This is not always true, though; the user may want to burn a file that is too large to fit on a single CD or DVD. In this case, disc spanning may split the file into sections, with each section able to fit on one medium. While common, sectioning is not a feature included with every burning program.
Disc spanning makes burning many files much easier, so it is a common feature included on many burning programs. It may even be included in the native burning program on an OS, or the program that comes with the OS. At the same time, some burning programs lack this feature.
The purpose of disc spanning is to make burning much easier for the user. Without this feature, a user typically would have to group files manually. This means he would need to check each file for its size to ensure the group can fit on a single medium, or he may have to condense one large file into sections without the help of disc spanning. At the same time, this feature does not always ensure that the files are properly burned; sometimes only the first medium burns correctly, while the others have information that ends up being corrupted.