A DVD-9 disc is a data or video DVD with two layers that hold information, allowing it to store approximately twice as much data as a standard single-layer DVD. This increased storage capacity allows you to use fewer discs when backing your computer up, and also allows you to store multiple movies on a single disc. However, DVD-9 discs have cost and speed drawbacks.
Technical Information
- A DVD-9 disc -- also known as a dual-layer DVD -- has two surfaces that store data, one under the other. After burning or reading the first layer of a DVD-9 disc, a DVD drive adjusts its laser to access the second layer of the disc without altering the first. When you insert a DVD-9 disc into your computer, Windows reports that it has 7.95GB of available storage. However, the disc's package may display a storage capacity of 8.5GB. This discrepancy is due to the difference between the decimal and binary systems of quantifying computer data.
Compatibility
- Hardware manufacturers began to introduce dual-layer DVD drives during the mid-2000s, and now most DVD drives support DVD-9 discs. However, if you have a DVD drive manufactured before the mid-2000s, it may not support DVD-9 discs. Look for an emblem such as "DVD-DL" or "DVD Multi-Recorder" on the bezel of a DVD drive to confirm dual-layer support. In some cases, it may be possible to convert a single-layer DVD drive to a dual-layer drive by installing new firmware.
Drawbacks
- Even the least expensive modern DVD burners can burn DVD-9 discs. However, a single DVD-9 disc tends to cost slightly more than two DVD-5 discs, so you may spend slightly more money if you exclusively buy DVD-9 discs for data storage. A spindle of 50 DVD-9 discs has a per-unit cost of approximately 64 cents when purchased from a discount retailer, while a spindle of 50 DVD-5 discs has a per unit cost of approximately 22 cents. Speed is an additional drawback of using DVD-9 discs: a typical high-speed DVD burner writes data at up to 24x when using DVD-5 discs, but burns DVD-9 discs at a much slower speed of 12x. Therefore, DVD-9 discs may take up to four times longer than DVD-5 discs to fill completely with data.
Comparison With Other Formats
- A DVD-9 disc holds considerably more data than a DVD-5 disc, which holds 4.37GB. However, it holds slightly less than a DVD-10 disc, which holds 8.75GB, or a DVD-18 disc, which holds 15.9GB. While a DVD-9 disc has one side with two layers, a DVD-10 disc has two sides with one layer each. A DVD-18 disc has two sides with two layers each. The primary benefit of burning content on a DVD-10 disc rather than a DVD-9 disc is compatibility, as some computer DVD drives cannot read or burn content on dual-layer discs. These drives can handle DVD-10 discs because each side is the same as a DVD-5 disc.
