About DVD formats...
DVDs are high-capacity CD-like optical storage media. A DVD holds up to 4.7 GB, while a CD holds just 700 MB.
DVD devices come as "readers" (DVD-ROM), and as "read-writers" DVD+R and DVD-R. It seems that DVD+R is preferred as the media of choice.
"DVD-R/RW was developed by Pioneer. Based on CD-RW technology, it uses a similar pitch of the helix, mark length of the 'burn' for data, and rotation control. DVD-R/RW is supported by the DVD Forum, an industry-wide group of hardware and software developers, and computer peripheral manufacturers. The DVD-R format has been standardized in ECMA-279 by the Forum, but this is a private standard, not an 'industry' ISO standard like the CD-R/RW Red Book or Orange Book standard."
"DVD+R/RW is also based on CD-RW technology. DVD+R/RW is supported by Sony, Philips, HP, Dell, Ricoh, Yamaha, and others, and has recently been endorsed by Microsoft. DVD+R/RW is not supported by the DVD Forum, but the Forum has no power to set industry standards, so it becomes a market-driven issue."
"DVD+R allows multiple layers for one disc where as DVD-R only allows one layer. Multi-layer DVD+R can allow extra capacity per disc than DVD-R hence its higher cost."
Dual layer refers to a more expensive DVD blank that can be written on two layers, hence the capacity is doubled - to about 8.5 GB.
A general comment about re-writing (RW)...
It has been my experience that data on RW media can be lost when these media are re-written to. It seems that the software adding new data mistakenly overwrites the file information already on the media, or the software somehow fails to properly append the new data. The result is an unusable disk, hence lost data. Since the cost of blank disks is just pennies, I recommend using write-one-time media, and I recommend making two copies of anything important.
Additions can be made to write-one-time media if all the space has not been used up already. When creating CDs (or DVDs), "finalize the session", but do not "close" (to future writing), the disks.
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