I was burning a CD-R the other day and got a "buffer underrun" error. The CD was useless and I had to start over. What causes that?

The short version: Your computer didn't send information to the CD-R fast enough.

The long version: CD-R drives put information from your hard drive into a "buffer" (i.e. memory area) before they write (copy) it to the CD. The idea behind a buffer is to maintain a steady flow of information to the unit.

When you burn a CD, it's done on the fly. The CD-R drive tries to keep its buffer full (or close to it) at all times. As long as there is information in the buffer, the CD-R drive can write to the CD.

If the buffer gets emptied out and not refilled (usually due to the computer being busy with something else) the CD-R drive has nothing to write to the CD that's spinning inside of it. Unfortunately, a CD has to have information on every section that's written, so you end up with the buffer underrun error and (in most cases) a CD-R disk that's as worthless as a 286.

To help prevent this problem, don't mess with your computer while it's writing to a CD (you may want to disable your screen saver too).