Mac Musings
What Is DVD-RAM and Why Would I Want It?
Daniel Knight - 2005.09.28
The revised Mac mini includes an 8x SuperDrive that supports DVD-RAM (although Think Secret is reporting that Apple may have disabled access to the feature).
What is DVD-RAM, and why should you care?
DVD-RAM was the first recordable DVD media Apple used - way back in the hoary days of 1999. The blue & white Power Mac G3 optionally came with a DVD-RAM drive that could store 2.6 GB of data per side. And boy was it slow!
If I recall correctly, it took about 90 minutes to fill one side of a DVD-RAM disc.
That was then. This is now.
We live in a world of high speed CD and DVD burners, and DVD-RAM technology has improved as well.
What Is DVD-RAM
CDs and DVDs record all of their data in one long track, much as vinyl records do. The drive can jump to any point along that track, but the single-track nature of these media makes truly random data writing impossible. You can have multiple sessions, but you can't rewrite a file.
DVD-RAM works more like a hard drive. There are lots of tracks, and each track has many sectors. Data can be read randomly, as on DVD and CD, but also written randomly, which these other media don't support. Thus, DVD-RAM is more like a floppy disk, a Zip disk, or a magneto-optical disk.
The original DVD-RAM specification supported 2.6 GB per side, while the DVD-RAM 2.0 specification supports 4.7 GB per side - the same amount as a recordable DVD.
Your Mac treats DVD-RAM like a removable hard drive, so you don't need special burning or mastering software to store your files. Nor do you have to burn all your information at once, as with writable CDs and DVDs. With DVD-RAM, it can begin writing immediately.
How Big Is It?
DVD-RAM discs look like CDs and DVDs. Same physical size. Same shiny finish. But with 4.7 GB of capacity, that's 6-7x as much data as a writable CD can store.
How Fast Is It?
DVD-RAM was horribly slow in the old days. The only reason the publisher I worked for used it was that we had some projects too large for 1 GB and even 2 GB Jaz disks.
The DVD-RAM drive Apple uses in the Mac mini supports 5x burning, which is roughly equivalent to 45x burning to CD. That's a transfer rate of 6.6 MB/sec.
That's approximately 400 MB/min. or 24 GB/hour. You should be able to fill a DVD-RAM disc in as little as 12 minutes. At least that's the ideal.
What's It Good For?
DVD-RAM is becoming popular on DVD recorders, and some newer DVD players will let you view content burned to a DVD-RAM disc.
But for computer users, DVD-RAM is an awesome backup medium. Got 14 GB of data in your user folder? You can back it up to 20 CDs or just 3 DVD sides. And by choosing DVD-RAM over DVD±RW, you can use synchronization software to add, delete, and replace modified files - no need to rewrite everything.
Is It Economical?
DVD-RAM is more expensive than other DVD media. Where you can get DVD±RW for about $1 a disc, you'll pay about 4x as much for DVD-RAM discs.
If you're simply archiving data, DVD±R media probably makes the most sense. You can burn at 16x, and since you're archiving, there's no need to choose rewritable media.
If you're doing a regular data backup, DVD±RW is cheaper and almost as fast as DVD-RAM (4x vs. 5x). But you'll be spending a lot more time writing data because DVD isn't a random-write medium.
DVD-RAM wins when it comes to updating your backup, synchronizing the data on your hard drive with your backup set. It only has to erase what's been deleted, add what's new, and replace what's been changed. It doesn't have to rewrite everything - my biggest complaint about CD-RW.
Is It for You?
I back up to external FireWire hard drives. I like the speed, the portability, and the fact that SuperDuper will even let me boot from my backup drive. It's not an inexpensive solution, though, at about $100 for the drive and $30 for an enclosure.
If I had a SuperDrive that supported DVD-RAM, I'd need about 16 single-sided or 8 double-sided DVD-RAM discs for backup. That would cost about $65 - half as much as my FireWire drive solution.
Of course, I'd have a stack of discs to deal with instead of a single drive, but I wouldn't have to remember to carry a power cable, power supply, and FireWire cable along with an external hard drive.
Then again, I couldn't make a bootable disk image on DVD-RAM.
Six of one. Half-a-dozen of the other.
You'll have to do your own analysis, but if you have a Mac with DVD-RAM support, it can be a great way to backup and sync your files efficiently.