[cctalk] Re: Dysan Alignment and Performance Testers

On Thu, 3 Oct 2024, Chuck Guzis via cctalk wrote: An analog alignment disk would be an impressive task. Something similar to the Dysan Digital Diagnostic Disk would be far more straight forward, starting with modifying a drive to be able to do precise (micrometer) postitioning of the head away from the normal position. Although far less precise and accurate than the analog alignment disk, . . radial alignment is done by seeing which off center tracks the drive can read. and adjusting it until it can read the same amount off-center in both directions. If it can read disks off-center in one direction better than disks off-center in the other diraction, that tells you which direction the head/positioner needs to be moved. The REAL dysan Digital Diagnostic Disk puts sectors on one track progressively further out of position in alternating sides; calling for reading an equal number of even numbered and odd numbered sectors. THAT would be difficult, but recording entire tracks off alignment by a known amount isn't so hard. Some of the old-timers might remember a guy who was on this list a long time ago, who claimed that the "copy-protectin defeating" program that he used could copy ANYTHING, even alignment disks! 'course, he was also the one who claimed that his 1990's "Sentry 7?) machine was the one that email had been "invented" on, that Valtrep was the predecessor to FORTRAN, and that he had a tape of OS/2 for the PDP(labeled "PDP OS/2"). Some of us speculated that that MIGHT actually be a backup tape from somebody having been using a PDP to develop some software to run under OS/2 -- Grumpy Ol' Fred cisin(a)xenosoft.com