Sony will ship blank dual-layer Blu-ray Disc media in June, the consumer electronics giant said today. But anyone hoping the arrival of 50GB discs will prove more economic than the now-shipping 25GB, single-layer discs is going to be disappointed.

Sony is now shipping 25GB BD-R and BD-RE media and expects them to cost $20 and $25, respectively. But while the 50GB versions due to ship in June provide double the storage capacity, they're more than twice the price. At $48 and $60, the 50GB BD-R and BD-RE media are 140 per cent more expensive than the lower-capacity discs.

If that increase were applied to Apple's iPod Nano line, for example, and using the $149 1GB model as a baseline, the 2GB model would cost $358 and the 4GB model $858, not $199 and $249.

To be fair, that's a fun comparison, but not an appropriate one. Dual-layer media tends to be more expensive than single-layer discs, in part due to the greater complexity of manufacture. A pack of 25 DVD+Rs might set you back $13, a cursory survey of online prices suggests. The same number of DVD+R DL discs from the same vendor would be priced at around $48 - a much greater mark-up than the jump from 25GB to 50GB for BD-R.

Still, the 25 8.5GB DVD+R DLs offer 4.25 times as much storage capacity as a single 50GB BD-R, but then you don't have to swap discs in and out.

And Sony - and other BD-R media makers, for that matter - can claim the advantage that it has the only recordable and rewriteable next-generation optical discs on the market. There's no sign yet of HD DVD equivalents. ®