What Type Discs - and System DVD Backup Problems

Question

I am very new to Macs and like many others here, I am a convert, after 18 years of using both MS-DOS and Windows based machines.
What a difference this iMac is, very impressive, but I am slightly miffed I missed out on the Intel Mac by a few days (literally).
Anyhow I have a few questions I am hoping you might be able to assist me with:
1. I do not know what the difference is between single layer type discs and any other type.
2. I do not know the difference between DVD–R and DVD+R type discs and which I might choose for what application. (I know the RW types are for reading and writing to repeatedly)
3. How do I do a “Multi-session” to a CD+RW or DVD-RW Disc? I have quite a few of these from my PC days and when I used one on my G5 I used the ‘Burn’ option in Finder to add a few small files. Unfortunately after I burned the files to the disc, I found I could not add any more later. In Windows, I could use these types of discs by just dragging files on and off no matter how many times I wanted.
4. My biggest problem is backing up the two Apple system discs that came with my iMac G5 20” (iSight).
I have purchased some Apple branded DVD-R discs which are 4.7 GB in capacity, but the Apple System (Install) disc 1 is 5.59GB in size (according to Get Info).
I have tried using the DiskUtility program to make an image using the DVD/CD Master option. This will make the Disc Image but of course when it comes to writing it to the blank DVD disc it states that the disc image is too big for the supplied media (the 4.7GB DVD).
Does anyone here know how I can back this disc up please, because I am worried that it will become damaged or scratched over time, no matter how careful I am with it?
All help and advice appreciated.
Drusus

Answer 1

Welcome to the fold!
You ask some good questions and ones that a lot of people do not know the answers to since they have just never run into the technology.
A single or double layer DVD is just like it sounds. One can write one layer of data on a disk (about 4.7GB) and the other can actually write on two layers one the same side of the disk for a total of about 8.5GB of data.
The difference between the -R and +R disks is not as crucial as it was when DVD recording technology was in its infancy. When the tech was being developed, home DVD player manufaturers chose the -R format while computers went with the +R format. Nowadays, most DVD players and computers will read and write both types of disks, but if you are making a DVD movie for grandma for whom you bought a DVD player 5 years ago, you will want to use the -R disks as her player will most likely not read the +R disks.
There is no way to burn a true multisession DVD in Mac OS X. Sorry. You can follow Ken Stone's process for burning a multisession CD though.
I suppose if you buy dual-layer DVDs, you can make that image of the install DVDs, but since I have used them exactly once in the last 2 years, I am not worried about them becoming damaged.