Modern CD copiers or CD and DVD burners they're more commonly known and have become ubiquitous in most personal computers and consumer entertainment centres. This has led to a general lack of understanding about what the difference is between professional CD and DVD burners and home-use CD and DVD burners. All CD copiers use a similar system of tuned lasers that encode data into an organic dye layer on the writable surface of a CD-R, changing how they reflect the reading laser and therefore creating readable marks. DVD burners use the same system, differing mainly in how the timing is laid out and the size of the reading and writing lasers. Rewritable CDs and DVDs use a special metal alloy which can melt and change up to 1000 times, which are useful for those using personal CD copiers to transfer data from one location to another, or backup files.
CD copiers all come with a speed rating, which is determined by the speed at which the spiral of the disc passes under its recording head, meaning how quickly you can transfer a certain amount of data. Early CD and DVD burners were called "Constant Linear Velocity" drives, because they would increase and decrease the rotation of the CD as the write head moved from the center ring to the outer ring of the CD- this meant that the disc would pass the recording head the same number of times. The maximum speed for a CD burner is 52x, because of the force of rotation- any higher, and the disc would literally shatter inside the drive. Most modern CD and DVD burners use variable speeds to keep the disc in safe levels of rotation.
Buffer underruns are a problem with common home CD and DVD burners, as the home computer could not keep up with the input/output levels to the CD copier; this meant that there was not a steady stream of data to the CD copier, leading to a forced halt of the recording process and an unfinished track. Newer, top of the range CD and DVD burners now include buffer underrun protection, which can stop and resume the burn process with built-in error correction.