July 31, 2012 – Control Data Diskettes Part II

July 31, 2012 – David Cooper vs. Control Data Diskettes Part II



 David Cooper is having some luck with the Control Data diskettes. It seems that these Control Data disks treat a disk drive exactly the same way that an moldy diskette treats a disk drive; when you insert them they sound like sandpaper, and the bumps are enough to get caught on the drive head, flake a little, which then turns the drive head into a rough surface which cuts more out of the disk, which flakes more, which coats the head more, etc. With the Control Data disks, though, it also seems that they had some serious issues with adhesion, and this process wears deep grooves in the disk almost immediately. With this, the disks seem to be only readable once (or at least, you cannot re-read and then re-re-read them), so it is basically a handful to read them. David is going to look into modifying CW2DMK to cache good read sectors (and then write out the best compiled sectors, rather than simply the random number of sectors that happened to read when the retry counter ran out) and to allow for starting at a specific track, both of which are somewhat necessary to get through many bad disks, but neither of which are not currently supported.

How is David reading them? He tries to pre-clean the diskette with alcohol to get as much of whatever is on these disks off as possible. Mind you, there are no visible stains on these disks to give a hint that this would need to be done. If one can get enough of the mystery goo off the disks, they won’t flake and they won’t clog the head, carving chasms into the diskette. Unfortunately, the disks also aren’t very good at retaining data, so once the errors creep up, he cleans the head again and tries again. This process will be smoother when/if CW2DMK is modified.

David may put together a video on how to clean a diskette; but his general theory is to apply rubbing alcohol to the exposed area, and then manually turn the disk by hand by grabbing inside the ring and applying gentle pressure to the diskette jacket to use the cloth inside to spread and clean the disk. Of course, if this brand of disks was not bad enough, the center reinforcement ring pops off at the slightest bend, so be prepared for that to happen too.

To clean his drive, he uses an actual 5-1/4 inch disk cleaner and uses the “clean” feature of imd.exe to step the heads back and forth in a good motion of disk cleaning.

I have never been successful cleaning a disk, and to clean my heads after a good coating, I just use que-tips and rubbing alcohol. I keep the screws out of the drive, and any time I start getting progressive errors, I simply pull the drive out (still connected), wet the que-tip, and clean the head. Of course, YMMV and I usually keep a decent supply of spare disk drives around because such rough treatment can only go so far.

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