On 02/01/2018 09:39 PM, Fred Cisin via cctalk wrote: > When I first got a Micropolis drive, I found "100tpi" hard to believe. > But, interchange attempts showed that by the inner tracks, it was not > 96tpi, and nor a multiple of 48tpi. > My homemade developer, and my patience to keep trying weren't good > enough to be able to successfully do other than take their word for how > many. > (Seeing the difference between 96tpi and 100tpi should be easier than > telling the difference between Leica thread (39mm x 26 Whitworth threads > per inch) V the early Russian Fed (39mm x 1.0m DIN thread) > some of the earliest Canon imitations (39mm x 24tpi thread))
Other than a brief encounter with an SA400 (single-sided 48 tpi. 35 cylinders), the Micropolis 100 tpi drives were my first real run in with 5.25" drives. Great drives, heavy, built like a tank--and expensive. I've got a late-model 96 tpi Micropolis that illustrates their NIH mindset--the PCB pivots as you close the door latch. Still used the precision-ground leadscrew positioner. Buffered seek; something like 4 steps per cylinder, if you can believe it. ISTR that if you stick a formatted 100 tpi ddisk in a 96 tpi drive and do a read ID, the first cylinder reads as 6. That is, the 100 tpi disk is offset a bit more toward the outside of the disk. You can read a few cylinders after that, before the misregistration causes things to get weird. --Chuck