info-mac@uw-beaver (02/01/85)
From: Hans.Moravec@CMU-RI-ROVER What's all this I hear about dirty disks? I looked at my most heavily used ones, and found the little comets on the upper surface. I also too apart a couple of bad Sony disks (two of my first 50 had bad spots fresh from the box). First of all the comets were on the UPPER surface of the disk - but the data storing oxide is on the LOWER surface. My guess is that the spinning motor emits a faint aerosol of oil droplets that land on the upper surface and are smeared into the comets when the spinning disk rubs against the case. Nothing to panic about, I think. The LOWER surfaces had no comets, but did show concentric tracks like tree rings of differing polish. This, I'm sure, is the effect of the head gliding over different tracks for differing lengths of time. Again, everything seems OK. Secondly, both the upper and lower internal surfaces of the hard plastic case of the Sony disks (I haven't taken apart any other brand) are lined with textured disk cleaning tissue. The tissue is very clean in my disassembled disks, but that's no surprise because they have not been used. Someday I'll sacrifice a good old disk to see if it gets very dirty with time. Overall, I don't think drive cleaning is all that important, except for the profits of cleaning kit manufacturers. -- Hans Moravec