20 Mar
2013
20 Mar
'13
12:56 p.m.
On Tue, 19 Mar 2013, Tony Duell wrote:
No. Assuming you're talking about the normal PC formats of those
capacities, the only differece is the number of cylinders. The have the
same rotational rate, the same data rate and encoding, etc.
Now, incorrect termination may cause ringing or reflections on the cable.
About the only place it is likely to matter is on the data lines (RD and
WD), and thosecarry the same frequencies for PC 360K and PC720K format.
About the onyl way it coudl matter is if the 360K and 720K drives are
different makes and one is more susceptivle to signal line ringing than
the othter.
Incidentally, later PC drives had fixed 1k pull-up resistors on all
inputs, no termination at all. Although it sounds like it should be a
problem, I have 2 such drives on an _external_ cable on a 5160 with no
trouble at all. No termiantio no nteh end of the cable.
I suppsoe a marginal set-up might work at DD (360K, 720L) rates but not
at HD (1.2M, 1.44M) rates. I think you'd really habve to tweak the cable
lengths to get a problem though.
For the pedants : Yes, I know that 1.44M makes no sense at all as a
number of megabytes of storage,. I am using it just as a name here.
-tony
WHile I agree that electrically the terminator
should be in the last
deive on the cable (furthest for mthe controller), has anybody ever had a
problem with it being in the 'wrong' drive on a fairly short ribbon cable
(as here)? That is, you ahve one termination resistor pack in the drive
enarest to the cotnrolelr and a 6" or so 'stub' linking to the second
drive.
As I said, electrically it's the wrong thing to do, but I've
(accidentlaly) done it a few times and the machine has had no problems.
Could incorrect termination account for inability to format "360K"
diskettes as "720K"? :-)