On 2009-04-30, Michael A. Terrell wrote:
"DoN. Nichols" wrote:
On 2009-04-30, Ivan Vegvary wrote:
[ ... ]
I bought my Wang used from an engineering competitor. It had an IBM
selectric input/output, along with a flatbed plotter. Two Memorex floppy
drives were attached. One of the floppies (not the drive) went bad and had
to buy a new disc. $ 800 for an 8" floppy (yes, they were floppy in those
days) that had a capacity of about 160K.
Hmm ... soft sectored or hard sectored?
The 8" floppies which I used on my SWTP systems we
250 K (SSSD)
500 K (SSDD)
1 M (DSDD)
but some systems used the 8" floppies as punched card images, so a 128
byte sector would only usefully hold 80 bytes, so that would take a SSSD
from 250K down to 160 K.
[ ... ]
One of the Metrodata computers used a SMS 8" drive system that held
500K per disk.
O.K. Either SSDD, or DSSD depending.
We ran them as master slave, because we could just barely
squeeze everything into 500K and could make a backup every day without
unlocking the CATV headend where the computer was. (The headend was
kept at 65 degrees F, year round) I replaced the master floppy once a
month by moving it from drive 1 to drive 0 and formatting a new disk in
drive 1. Then when the day's backup was made, we archived the old disk
for emergencies. The damn Shugart 801 drives ran 24/7 and wore out in
about two years. Every new drive had a different PC board, so we had to
make several phone calls to get the configuration data every time a
drive failed. The SMS design didn't lift the arm when it wasn't in use,
O.K. This makes it SSDD (Single Sided Double Density), since
the Double Sided drives moved one head against the other closing onto
the surface of the floppy. Those *might* have lasted longer in a clean
environment. (Of course, a bit after the Mt. St. Helens eruption, 8"
(and 5-1/4") floppies were having problems because of the airborne
abrasive dust which it spit out.
so the felt pads would wear out. Then the arm would stick to the disk
and destroy the floppy.
Ouch! I *never* had an 8" floppy drive wear out -- but the OS
and controller lifted the heads when not actively reading or writing.
I *did* have a DSDD 5-1/4" floppy drive die -- but from poor
design. The centering cpu was on a 1/4" shaft, running through two
shoulder style ball bearing assemblies, and secured by the drive pulley
slid onto the shaft, and then a central screw and washer tightened to
grip, followed by a glob of Glyptal to secure it.
Note that I didn't mention a spacer between the inner races?
The shoulders spaced the outer races out on the cylindrical bore, but
they depended on tightening the screw beyond slip onto the pulley, which
resulted in a serious end load on the bearings. When I discovered the
problem, it was when some new OS disks could not be read (the previous
ones were 8", and these were 5-1/4"). Once I pulled the drive, I could
feel the bearings cogging when I tried to turn the spindle.
So -- I got some new bearings (again with shoulders) dis some
measuring, and machined up a spacer (actual metalworking here :-) to go
between the inner races. I left about 0.001" of end float when the
screw through the pulley was cranked down tight -- since the centering
cup was held biased by the centering cone which held the floppy in
place. Once that was done, I got lots of life from the drive. I wish
that I could remember who made that drive. For a long time it was my
only double-sided 5-1/4", and kept company with three single-sided
Shugart 5-1/4" drives (and two 8" DSDD drives on the same system.)
Somewhere I should have a pair of Teac 1/2 height 8" DSDD drives that
don't need 120 VAC.
Hmm .... there was also the one used in one of the sytems which
had a voice-coil servo for head positioning, instead of a stepper motor.
I never had one, but I understand that while they were noticeably faster
on track-to-track seeks, the also needed to be re-aligned fairly often,
while the Shugarts were rock solid as far as alignment goes.
Enjoy,
DoN.
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