Originally Posted by
Jim Andrada
Well a lot of times it IS crashing - but crashing in a controlled way. As in bumping into the so-called Crash Stops that determine the limits of travel. I don't know the details of these particular scanners, but it isn't (or wasn't in the old days when I used to write firmware to control mechanisms) for the machine to lose track of it's location, in which case the firmware would drive the head in one direction until it encountered some resistance - and at that point it would probably back the head away and drive it forward again several times to be sure that it really was at the limit and not just running into a random piece of dirt. Producing a sort of loud rattling sound. Before they had textured "landing zones" or other ways to take the heads of a disk drive off the surface for shutdown. the heads would land on a portion of the disk that had a lubricant coating and sometimes if they sat there long enough capillary action would suck lubricant into the head - disk interface and sort of glue the heads to the disk. At startup they's have a routine that would try to unstick the heads by banging them hard agains the crash stops and it would make quite a racket while breaking the heads loose. And in a really bad case the heads would stay stuck to the disk and the machine would actually tear the heads off of the suspension arms.
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