How to write resumes?

A buffer underrun occurs during recording if the recorder runs out of data in the buffer. Once the laser is on, it cannot stop and resume flawlessly; thus the pause necessitated by the underrun can cause the data on the disc to become invalid, and thus unusable. Since the buffer is generally being filled from a relatively slow source, such as a hard disk or another CD/DVD, a heavy CPU or memory load from other concurrent tasks can easily exhaust the capacity of a small buffer. Therefore, buffer underrun protection was implemented by various individual CD/DVD writer vendors. With this technique, the laser is indeed able to stop writing for any amount of time and resume when the buffer is full again. The gap between successive writes is extremely small.