CD-RW

Authoring

A CD-RW’s data layout changes during and after writing. It includes a Power Calibration Area (PCA) for setting the laser’s correct power, a Program Memory Area (PMA) that acts as a temporary table of contents for an open session (recording up to 99 audio tracks or data file addresses), and a Program Area (PA) holding the actual audio or data. The PCA and PMA together form the System User Area (SUA). Each session on a multi-session disc has a lead-in, PMA, PA, and lead-out. When the session is closed, the PMA’s table of contents is moved to the lead-in, and the PCA and PMA are logically removed.

Speed specifications

CD-RW discs have hardcoded speed specifications that limit recording speeds to restrictive ranges. Unlike CD-R, a CD-RW has a minimum writing speed below which recording is not possible, due to the phase change material's heating and cooling time constants and required laser energy levels. Some professional audio CD recorders, such as those made by Tascam, use special techniques to bypass these limitations and can record high speed discs in realtime.

Writing too slowly or with too low energy on a high speed unblanked disc prevents proper blanking, while excessive laser energy causes overheating and insensitivity to data. Older CD-RW drives lacking appropriate firmware and hardware are incompatible with newer high-speed discs, but newer drives can record to older discs if their firmware can set correct speed, delay, and power settings. Reading speed depends primarily on the reading drive's capabilities, not the disc's speed specification.

Many half-height CD and DVD writers from 2004 to 2010 officially supported CD-RW UltraSpeed Plus (32× Z-CLV), while more recent DVD and Blu-Ray writers have downgraded backwards compatibility to CD-RW UltraSpeed (24× Z-CLV). Slim type optical drives usually support CD-RW writing speeds of 16× or 24× Z-CLV in zones of 10× CLV, 16× CLV, 20× CLV and 24× CLV towards the outer edge.