-ROM, -R, +R, +RW? Understanding the optical drive alphabet soup

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Nick248 asked the Answer Line forum about optical drives. I figured it was time to go over the various types of CDs, DVDs, and Blu-ray discs, and the drives that read and write to them.

[Email your tech questions to answer@pcworld.com or post them on the PCW Answer Line forum.]

I can't blame anyone for being confused. We've got three types of optical discs (CDs, DVDs, and BDs), with five different capacities between them. There are discs you can only read from, discs you can also write to, and discs you can write to, erase, and write to again. And the acronyms aren't always helpful.

Let's start with the acronym that appears before the hyphen, which tells you the standardized disc format:

CD-: Compact Disc. These hold about 700MB of data. A CD drive can only read or write CDs.

DVD-: Digital Video Disc or Digital Versatile Disc. They usually hold about 4.7GB. DVD drives can also handle CDs.

BD-: Blu-ray Disc. This has to be the worst tech acronym since FLOPS. I mean, shouldn't there be an R in there somewhere? Fortunately, they're often called Blu-ray drives and discs. They usually hold 25GB. The drives are CD and DVD compatible.

The acronym after the hyphen tells you what you can do with that type of disc or that type of drive.

-ROM: Read-Only Memory. You cannot write to a -ROM disc, which left the factory with data already on it. A -ROM drive can read discs but not write to them, and has no use at all for a blank disc.

-R: Recordable. You can write to one of these discs once (provided you have an -R drive). But when you're done, it's effectively a -ROM disc.

-RW: Rewritable. Another stupid acronym, that always suggested "read and write" to me. You can write to these discs, erase them, and write to them again.

-RE: Recordable Erasable. The Blu-ray variation of -RW, with a far more sensible acronym.

Here are a few other terms you may want to know:

Burn: Write to a disc. It's called burning because it's done with a laser, not a pen.

DVD+R; +RW; ±R, ±RW: There are two standards for recordable and rewritable DVDs: DVD-R and DVD+R, each with its equivalent RW variation, and each requiring its own type of drive and blank disc. The ± sign, which you'll only find on drives, tells you that the drive can burn both - and +. Virtually all drives these days are ±, making the difference between +R and -R irrelevant.

DL: Dual Layer. This doubles or nearly doubles the capacity of DVDs and BDs. A DVD DL can hold about 9GB; a Blu-ray, about 50GB. To burn discs with these capacities, you need DL discs, plus a DL drive. Any DVD or Blu-ray drive can read DL discs.

Read the original forum discussion.

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