denoted as the System User Area. Each session on a multi-session disc has a corresponding lead-in, PMA, PA and lead-out. When the session is closed TOC information in the PMA is written into a lead-in area and the PCA and PMA are logically eliminated. The lead-out is created to mark the end of the data in the session. Speed specifications Like a CD-R, a CD-RW has hardcoded speed specifications which limit recording speeds to fairly restrictive ranges. Unlike a CD-R, a CD-RW has a minimum writing speed under which the discs cannot be recorded, based on the phase change material's heating and cooling time constants and the required laser energy levels. Despite this, some professional audio CD recorders, such as those made by Tascam, use special techniques to bypass these limitations and can record high speed (but not ultra speed) discs in realtime. Since the CD-RW discs need to be blanked before recording data, writing too slowly or with too low energy on a high speed unblanked disc will cause the phase change layer to cool before blanking is achieved, preventing the data from being written. Similarly, using inappropriately high amounts of laser energy will cause the material to overheat and be insensitive to the data, a situation typical of slower discs used in a high powered and fast specification drive. For these reasons, older CD-RW drives that lack appropriate firmware and hardware are not compatible with newer, high-speed CD-RW discs, while newer drives can record to older CD-RW discs, provided their firmware correct speed, delay, and power settings can be appropriately set. The actual reading speed of CD-RW discs, however, is not directly correlated or bound to speed specification, but depends primarily on the reading drive's capabilities. Many half-height CD and DVD writers released between 2004 and 2010, including the TSSTcorp SH-M522 combo drive (2004), Pioneer DVR-110D (2005), Hitachi-LG GSA-4167 (2005), TSSTcorp SH-S182/S183 (2006) and SH-S203/TS-H653B (2007) have officially adapted support for CD-RW UltraSpeed Plus (32× Z-CLV), while more recent DVD writers such as the SH-224DB (2013) and Blu-Ray writers such as the LG BE16NU50 (2016) have downgraded the backwards compatibility to CD-RW UltraSpeed (24× Z-CLV). Slim type optical drives are subject to physical limitations, thus are not able to attain rotation speeds of half-height (desktop) optical drives. They usually support CD-RW writing speeds of 16× or 24× Z-CLV in zones of 10× CLV, 16× CLV, 20× CLV and