If you’ve ever wondered what “dual layer” (sometimes known as “double layer”) recordable DVD discs are, or what the issues surrounding their use are, read on!
At their simplest, dual layer DVDs have two data layers. This gives 8.4GB of storage space instead of the 4.7GB found in ordinary (single layer) DVDs.
Most pre-recorded commercial DVDs are dual layer, and have been for a number of years. However, until recently they’ve been less common in the recordable DVD market. Why?
Well, cost for one thing. For a long time, recordable dual layer discs were way more expensive than single layer ones- even taking into account the capacity. Typically, they cost £2-5 when single layer discs were more like a tenth of that. Fortunately, around 2006-07, prices started falling substantially. As of mid-2008 you can buy some for under 40p in bulk.
Byte-for-byte, that’s still a little more expensive than single layer media, but it’s worth it if you don’t want to have to spread data over two single layer discs, or compress your videos to fit.
Dual layer discs also tend to be slower in the recording department. Many cheaper discs are 2.4x recordable, with some at 8x. By contrast, virtually all single-layer discs are at least 8x recordable, with 16x versions costing not much more. On top of this, DLs can hold more data, so take longer to fill.
Main Types of Dual Layer Recordable DVD
There are several recordable DL DVD formats, but you’re only likely to come across two in the shops at present. As of mid-2008, the vast majority of discs on sale are DVD+R DL, with a smattering of its rival, DVD-R DL. Both are write-once (i.e. they can’t be re-recorded).
As with the original DVD+R and DVD-R, the reasons that two otherwise similar (but incompatible) formats exist are mainly commercial- they’re supported by rival groups of companies.
DVD+R DL came out first by quite a long way. This means that most burners built since early 2005 support the format (although please check yours if in doubt). There’s now a wide range of discs on sale.
DVD-R DL is a much newer format, and because of this it isn’t supported by older drives, and the discs generally aren’t anywhere near as widely-available.
Since -R DL doesn’t really offer much different to +R DL (and vice versa), in most cases we’d stick with the commoner and better-supported DVD+R DL. However, as always, check what your drive supports before choosing.
You may also wish to consider which discs have the best compatibility with (e.g.) DVD players.
Other Recordable DL DVD Types
There are other types of recordable dual layer DVD, but they’re all rare and/or poorly-supported at present. You’re unlikely to come across them in the shops.
DVD+RW DL and DVD-RW DL are the two competing rewritable formats. At present, it’s unclear whether either will grab a significant market share. Our gut reaction is that they’ll be supported by some newer drives and may enjoy minor success for this reason. However, we believe that ultimately they’ve been released a bit too late and that in the long term most people seeking high-capacity rewritable media will jump to rewritable Blu Ray discs instead.
There are no dual layer versions of the DVD-RAM format.
