CDC 5 1/4 floppy 77711501 / 77711800 specs

g-wright at g-wright at
Sun Dec 9 01:48:57 CST 2007

-------------- Original message from Fred Cisin <cisin at>: -------------- 

> On Sun, 9 Dec 2007 g-wright at wrote: 
> > Hi 
> > I have a machine with a 77711501 floppy drive and it's bad.. I have 
> > tried 3 different 360k drives. I tried to find specs on it but so far have 
> not. 
> > What is the difference between that drive and a 77711800 used in a PC 
> > The computer just says there is a drive error. I'm using the same jumper 
> > settings on both. I have also tried a Teac fd-55bv. 
> > Is it a 320k drive ?? 
> There ain't no difference. 
> 320K drive and 360K drive are the same drive. 
> There is a way that it would be possible to build a drive that could do 
> 320K, but not be able to do 360K, but nobody has done so yet. 
> Boot something other than WINDOZE. "Drive error" is not specific enough. 
And for the rest of the story .....................

This is on a MicroStar  machine that runs StarDos. I know nothing about this
but from recent posts I decided to drag one of them down and look into it a 
little further.  This machine I have running is a  Micro Five 1000 with a IMI 
10 meg HD. It  has a boot menu and back up Menu. It will still boot and 
will make its own formatted floppies and back itself up with out much 
problems.  If I try to read one of the floppies with Image disk or Anadisk
they fail.  It tried with both 360 and 1.2 meg drives.  I would guess that
the drive in the machine is off enough to cause these problems .  If  I
install another floppy drive, the System picks up something and errors. So
there must be some other signal or ??? coming from the drive.     The 
machine date is in the 84 -85 range

The straps on the drive (M 4 x 3 2 1 H) are set  with  M and 1 jumpered

- thanks, Jerry

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