A disc with two data layers, allowing it to hold almost twice as much data as a single layered disc. In the past, dual layered discs were readily recognizable by their gold colouration, but this has changed recently due to a change in manufacturing process and many dual layered discs are now silver, the same as their single layered counterparts. The layers can be laid out in one of two fashions; Opposite Track Path (OTP, more commonly known as RSDL - Reverse Spiral Dual Layer), where the first layer runs from the inside of the disc to the outside and the second runs from the outside to the inside, or Parallel Track Path (PTP), where both the first and second layers run from the inside of the disc to the outside. RSDL is often used for long programming, to minimize the time taken to negotiate the change in layers. PTP is often used where a widescreen and fullscreen version of the program co-exist on the same side of a disc. Dual layered discs are also known as DVD-9s.
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