Reader Chris writes: What do CD read, write, and rewrite speeds mean?

If you've ever bought an optical drive, you've probably noted a bunch of random numbers succeeded by the letter "X" on the box. What does 12x/10x/32x (also written as 12x10x32) mean?

In the beginning of CD-ROM, there were no Xs, because all drives ran at "1x,"  "X" refers to (roughly) 150KB per second, the original speed a CD-ROM was read at. Today, "32x" refers to 32 times that speed, or about 4800KB per second.

As writing capabilities emerged, followed by re-writing capabilities, additional speed ratings were added to drive descriptions, because a drive usually can't write at the same speed as it can read.

When looking at a trio of drive speeds like the one above, they refer to write speed, then rewrite speed, then read speed. You can fairly easily find a 52x32x52 drive today (most new drives are this speed), about the terminal limit for CD-RW devices.

DVD-RW drives use the same nomenclature, only, to make things even more confusing, 1x on a DVD drive is about nine times faster than 1x on a CD drive. However the write/rewrite/read breakdown still holds. Most new DVD-RW drives are in the range of 16x8x16, with slower speeds for dual-layer media.

Bottom line for all of these products: In general, buy the drive with the highest numbers for all three of them.