8" drive on a pc controller

<Please forgive my interloping, here, but my SHUGART and Siemens SD 8" drive <are spec'd for 6 ms step rate, and the double-headed types for 3 ms. It's <really best (mechanically) to step these babies as fast as they will go, an <it's quieter too. Be specific on the model as the sa800s and 850s would never do 3ms! Though the later ones did step faster. The problem with 8" drives are that there were some that were doing their best at 10-12mS and a few like CDCs 3ms was the norm. Most fell in around 6mS. ALSO, the PC controller uses the 765 chip (or it's core) generally and that chip can truncate the first step pulse by 1/2mS (8/5"). So the fastest recommended step rate programming (srthut in SPECIFY command) is 4mS. I believe it was never fixed. Allison