>with positioning. They now use voice-coil actuators rather than steppers,
>and therefore can make quite subtle adjustments in head-stack position
>depending on what is read. Back in the early days, that wasn't so.
Actually, Persci floppy drives in 1976 or so were voice-coil (and quite
a pain to maintain, even then - these days the glue that holds the
optical graticules in place is often failing, and gluing and realigning
from scratch is even harder, even with all the special Persci
realignment jigs and electronic panels.) And a common modification
to these drives (at least for folks like me who specialize in data
recovery) is software-controlled offsets from the normal track positioning,
something that does use the drive's ability to do fine positioning.
>One interesting thing about the Apple GCR modulation format is that it
>essentially was a "double-density" technique.
Eric said the same thing, and I disagree with you both. To me (and all
the tech pubs I've read) the density is how many flux transitions you can
do per second (or revolution). GCR is a way of getting more real data with
the same number of flux transitions. Apple GCR drives use single-density
heads and single density data rates, a considerable cost saving factor
in 1977.
>cost plenty back then. This was at a time when Radio Shack still stayed
>with single-density, and Apple exceeded their capacity easily.
While using cheap single-density drives!
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Thu Apr 08 1999 - 21:56:01 BST