The UDF file system was developed when it became increasingly obvious that the ISO9660 file system used on CDs was no longer meeting the needs of rewritable media and DVDs. It was optimized mainly to accommodate large data volumes and to make it easy to modify an existing file system.
Nero can burn UDF and so-called 'UDF Bridge CDs', which contain both a UDF and an ISO9600 file system. The UDF file system can be read by, say, Windows 98 and Windows 2000 with no special drivers. In case of doubt, Windows 2000 and Windows 98 also read the UDF file system if both an ISO9660 and a UDF file system are detected on the medium. Writing in UDF format is particularly important when burning DVDs because UDF is the preferred operating system for these media.