1.   If the lens is blocked by dirt, it cannot read the disk accurately, and that causes skipping or stuttering.

2.   If the recorder does not do that, a gap is created on the CD, and a CD player would not be able to read the disk.

3.   Such a photo would enable the optical drive to read the disk at up to a gigabyte per second.

4.   The disk can be read by putting another pulse through the tip and measuring the current.

5.   This is why they can read IBM disks.

6.   With multimedia disks, such problems can make it impossible to read the disk at all.