What is the capacity of a DVD+R ?

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I've a number of data files to backup to DVD+R

They are marked as having 4.7 GB capacity.

I know that the GB figure is being shown in marketers terms i.e. 4,700,000,000 bytes rather than based on 1k = 1024 bytes, but even so, the seeming maximum number of bytes I can save to each DVD+R is only around 2.5 GB!

Any ideas why the huge discrepancy? None of the individual files I'm wanting to backup to DVD are larger than around 100 MB maximum.

Vista shows that the blank disk has exactly 4,700,372,992 bytes free space.

If I attempt to drag and drop 3 GB worth of files to this blank disk I get a message saying: "There is not enough space on the DVD RW Drive. You need an additional 564 MB to copy these files."

It only wants to proceed if I reduce the number of files to a measly total of around 2.5 GB!

Any ideas what the problem is and if it can be worked around, or is the 4.7 GB claim a plain lie?

i think something is wrong with either vista.. or the app you use to burn with... or both.

http://en.wikipedia.org/wiki/DVD+R

The problem turned out to be a poorly worded error message from Vista! The problem wasn't the low capacity of the DVD+R as it was claiming, it was really that the hard drive C didn't have enough room to store the intermediate disk image that gets subsequently transferred to the DVD+R

Vista had gobbled up more hard disk space than I'd realised with its System Restore point backups and only left around 2.5 GB free space left on hard drive C. This meant the largest image size that could be created as the intermediate part of the backup to DVD+R was only 2.5 GB.

I've deleted all but the most recent system restore points and now have around 10 GB free space on the hard drive and now it is allowing me to drag and drop 4.7 GB worth of files to the DVD+R

The problem baffled me because I was sure I'd backed up large quantities of files to DVD before and never had this problem. I also got the same error message trying to use either the laptop's own DVD drive and an external USB DVD drive.

Anyway, problem now solved.

thus proving Windows Vista is donkey dung