Most modern CD/DVD writers implement some form of buffer-underrun protection. A buffer-underrun occurs when the writer's buffer (high speed memory built into the writer itself for organizing data prior to writing it onto the disk) become empty of data before the writing process is complete. This leaves the new CD spinning in the drive while no data is available to be written to it, resulting in the writer essentially 'losing its place' on the disk and creating a useless CD.

A buffer-underrun can occur if the computer's resources are being taken up by another process.

For example, significant use of the hard drive that is sending data to the writer by another program can break up the data stream going to the writer's buffer, resulting in an underrun. This potential problem was the reason that most early CD-burners recommended doing little else with your system while a CD was being created.

Various manufacturers have patented their own methods of avoiding this problem, Plextor's BurnProof technology being one example, but most work in a similar way: The drive, assisted by the burning software, monitors the amount of data in the buffer. If this falls below a certain level, and the CD is not yet complete, the drive suspends the writing process while taking a note of the area on the CD it was writing to.

Once a sufficient amount of data has accumulated in the buffer again, writing is resumed from a point very close to where it was originally halted. This effectively eliminates the problem of buffer underrun, though running intensive applications such as games while you are creating CDs is still not a good idea.

Using CD-RW media

CD-RW disks are written using the UDF file system, or 'packet writing' where individual sectors are written to the disk and referenced by a single, updated address table. This has the advantage, in current versions of UDF, of allowing individual sectors on the disk to be erased and rewritten.

Obviously, as the ability to be erased and written over is the main advantage of CD-RW disks, this is an important feature.

UDF is considerably more flexible than the ISO 9660 file system, removing the need for a finite session to be created each time data is added, making the media a lot more like a traditional hard disk. Physically, CD-RW media is different from CD-R media, but the specifications in terms of maximum rated write speed work the same way.

CD-RW disks will generally not play in standard audio CD players, unless specified, due to the lower reflectivity of the disks as compared to CD-ROMs or CD-R disks, and may not play in older CD-ROM drives as they often do not support the multiread specification, which essentially provides the ability to read less reflective media through the use of higher amplification.

The disadvantage of the UDF file system is compatibility. Most modern operating systems including Windows XP still do not read all UDF formatted disks. WindowsXP will read UDF disks burned by certain software, but not others.... To rectify this, you may need a UDF reader program, which will be included with the software if required. Many programs capable of burning UDF CD-RWs will include the reading software automatically on each CD created, so it can be installed when the disk is inserted.

CD-RW disks must be formatted with the UDF file system before they can be used, and this can be a time consuming process, usually between 20 and 40 minutes, depending on the speed of the CD-RW drive. Once this is done, the files can be dragged and dropped directly to the CD drive using the standard Windows interface.

There are several popular UDF CD-creation programs, most coming as companion software to traditional CD-burning software, Such as Direct-CD or Drag-To-Disk with Roxio's Easy CD Creator, or InCD with Nero. The websites for these companies also contain comprehensive information for formatting and using CD-RW media.