Rob Pegoraro, agony aunt for the digital age, answers computer users' questions.
Q: Why aren't there any rewriteable double-layer DVDs? I can find dual-layer discs only in write-once formats that I can't reuse.
A: Recordable DVDs can hold 4.7 gigabytes of data, and once that must have seemed like an inexhaustible capacity.
But now that one year's worth of digital photos can max out a disc, the 8.5 GB allowed by "dual-layer" discs looks a lot more attractive.
But the only dual-layer discs for sale are write-once blanks, not the more useful rewriteable kind.
That's not because DVD technology prohibits such a thing.
A few years ago, the DVD Forum, which sets industry standards, approved a set of specifications for dual-layer rewriteable DVD-RW media, and the same work has been done for the DVD+RW format.
But other factors hold back these higher-capacity rewriteable discs - starting with high prices and limited compatibility, said Hugh Bennett, an industry consultant in London, Ontario.
He said dual-layer rewriteable discs were expensive and inefficient to make, and they don't work in existing DVD players and drives.
Andy Marken, a spokesman for disc vendor Verbatim, pointed to the historically poor sales of rewriteable discs.
The sales of write-once CDs and DVDs have outpaced those of rewriteable discs by a factor of five.
That gives manufacturers little incentive to make dual-layer DVD-RW or DVD+RW formats work.
So how are you supposed to back up all of your photos?
The best high-capacity back-up tool remains an external hard drive that you can plug into any other machine - although it's a good idea to keep a second back-up of your most important files on a DVD.
