DVD CDs (0.74 µm for DVD versus 1.6 µm for CD), accounting in part for DVD's increased storage capacity. In comparison, Blu-ray Disc, the successor to the DVD format, uses a wavelength of 405 nm (violet), and one dual-layer disc has a 50 GB storage capacity. Read and write speeds for the first DVD drives and players were 1,385 kB/s (1,353 KiB/s); this speed is usually called "1×". More recent models, at 18× or 20×, have 18 or 20 times that speed. Note that for CD drives, 1× means 153.6 kB/s (150 KiB/s), about one-ninth as swift. DVD-Video is a standard
Optical disc drive inexpensive, are suitable where read/write capability is required. Disc recording is restricted to storing files playable on consumer appliances (films, music, etc.), relatively small volumes of data (e.g. a standard DVD holds 4.7 gigabytes) for local use, and data for distribution, but only on a small scale; mass-producing large numbers of identical discs is cheaper and faster than individual recording. Optical discs are used to back up relatively small volumes of data, but backing up of entire hard drives, which typically contain many hundreds of gigabytes or even multiple terabytes, is less practical. Large backups are often instead made on