Hi I meant to jump in earlier when we were talking about the data formats on disk but got side tracked with work ( ick! ). It was mentioned that one could have no more than two concecutive zeros. It was mentioned that this was a speed issue of the disk. Actually there is another reason. The level of the signal from the disk is constantly changing. Think of driving over a rough road and you want to count the rocks but not the larger bumps. If you just set a fixed threshold on the shocks, every time you went over a bump, you would miss a bunch of small rocks while the suspension system was absorbing the larger bump. Now, if you made the system track the slower larger stuff, you could ignore the large bump and still see the rocks. The problem is that the system now sees the occational rock when there was none for some time because it is drifting along. By making sure that there are occational rocks, the system can stay adjusted to be most sensitive to the rocks without having false detects. The disk read is the same, it needs to see data circuit from having false detects from noise and random level shifts. Dwight