2 Feb
2018
2 Feb
'18
6:17 a.m.
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