8 Aug
2011
8 Aug
'11
12:35 p.m.
The cable "twist" was a very clever (but not
original) solution to a
thorny problem of how one controlled the spindle motors on two drives
when there is only one motor control line. The fact that one could
also set all floppies to the second drive select was a bonus.
I always liked the way thatHP did it in the 9836 machines. Those have 2
5.25" floppy drives, permanenytly enabled (MX jumper fitted) amd linked
by separate ribbon cables to the controller board. The latter is fitted
acrsso the case behind the flopy drives which means the ribbon cable
layout is quite tidy.
This arrangement means that not only can the motors be controlled
separately, but also the write protect lines can be monitored in
hardware. Since chanigny a disk will always result in some transitions on
the QP line, this is used to provide a 'disk changed' signal.
You've led a sheltered life. All of my disk
products allowed for
configuration of port, IRQ and DMA channel.
I am pretty use I used 22disk and/or anadisk with the secondard
controller in thae 5160 under discussion (this controller goes to a pair
of 8" drives) before I started writing my own stuff.
As undergrads, many of us had access to a slide rule
and the "rubber"
book.
FWIW, I still do. I would not want to be without a Rubber Bible actually,
there's a lot of very useful information in there. OK, mine is now nearly
40 years old, but while the physical constants are now known more
accurately, the differences are unlikely to affect anything I am doing :-)
As for slide rules, I have several and know how to use them. I was lucky
enough to find an Otis King (helical slide rule).
-tony