Writing drives are real-time devices. Being a real-time device places special demands on a computer and its peripherals. For a writing drive to successfully create a disc, it must receive an uninterrupted flow of data that must be transferred at a speed equal to or greater than the recording speed of the writing drive.

For writing drives operating in CD single-speed (1x) mode, data must be transferred at a continuous rate of 150 KB per second for data, and ~172 KB per second for audio. For writing drives operating in CD double-speed (2x) mode, data must be transferred at a continuous rate of 300 KB per second for data, and ~344 KB per second for audio. For writing drives operating at 16 times the CD playback speed (16x), data must be transferred at a continuous rate of 2,400 KB per second for data, and ~2,752 KB per second for audio. For writing drives operating in DVD single-speed (1x) mode, data must be transferred at a continuous rate of 1,380 KB per second.

Data transfer rates in the above ranges are normally below the data transfer rates claimed by hard disk manufacturers. However, slow processor or bus performance and sub-optimal hard disk performance may combine to reduce the actual sustained data transfer rate below the transfer rate requirement of high-speed writing drives.

Every writing drive is equipped with internal memory used as a data buffer. The data buffer stores data as it arrives from the computer, and then transfers that data to disc. The size of the data buffer for an individual writing drive is critical for error-free recording. A slow-down in the transfer of data from the processor caused by high network traffic or the small interruption of a hard disk re-calibration can interrupt the recording process if the buffer is not large enough to "wait out" the interruption. If the data buffer empties (buffer under-run error), the recording process could fail and ruin all blank discs.

If your computer and peripheral devices are fast enough, you may be able to duplicate "on-the-fly". When recording on-the-fly, be certain that the reading speed is always equal to or greater than the writing speed. In cases where the speed of the input source is not fast enough to support "on-the-fly" duplication, an intermediate disc image file can be written to a hard disk. You should also be aware that the read speed for Audio CDs can be less than the marketed reading speed, a scenario resulting in buffer under-runs.