A small laser interferomenter and a screw driver could be used, once one determined the center of the track by magnetic material and a microscope. Some what special equipment but not all that special, now days. Years ago, I went to a Seagate building to help a friend with a servo writer problem. It only took a few minutes so I never charged them. Of interest here was that they used a stepper motor to control the position of the head. The problem was that they wanted to turn the power off to the stepper motor to remove an stray magnetic fields. They did it too soon while the motor was still in motion, causing the motor to not stop at the desired location. Adding some delay solved that one. So, the point is that a stepper was enough for a hard drive servo track. Of other interest, they were using an AIM 6502, running figForth. The programmer was obviously a previous BASIC programmer because he'd named vaiables with names like A, B, ... , instead of meaningful names that would have made the code more readable. Dwight
________________________________ From: Jonathan Chapman via cctalk <cctalk@classiccmp.org> Sent: Thursday, October 3, 2024 4:11 AM To: General Discussion: On-Topic and Off-Topic Posts <cctalk@classiccmp.org> Cc: Jonathan Chapman <li...@glitchwrks.com> Subject: [cctalk] Re: Dysan Alignment and Performance Testers > question: could somebody (did they at the time) write a program for the apple > ][ to create such a diskette? The apple drive can do half track stepping, and > IIRC the signal is written strictly by a timing loop in the program Not really. Merely half-stepping a drive wouldn't be accurate enough, plus you need to be able to drive not-data waveforms into the heads. --snip--
