Blu-ray Disc (BD) is a next-generation optical storage medium developed by Sony and others. It uses a blue-violet laser with 405 nanometre wavelength, and offers 25 GB (single layer) 50 GB (dual layer) storage capacity. Blu-ray discs appear as BD-ROM (read-only, pre-manufactured), BD-R (recordable once), and BDRE (recordable and erasable). The 1X data transfer speed for a Blu-ray drive is 4.5 Megabytes per second. The Blu-ray Disc format is not compatible with the other next-generation optical storage medium, HD-DVD.