5.25 floppies that read but don't write

dwight dkelvey at hotmail.com
Thu Aug 20 22:01:13 CDT 2015

> Date: Thu, 20 Aug 2015 13:57:05 -0700
> From: cclist at sydex.com
> To: General at classiccmp.org; classiccmp.org:On-Topic and Off-Topic Posts cctalk at classiccmp.org
> Subject: Re: 5.25 floppies that read but don't write
> On 08/20/2015 01:04 PM, Marc Verdiell wrote:
> > So I tried to force formatting in DOS at 360k, and sure enough it
> > worked! I can then read the diskette back, write on it, etc... And of
> > course it failed formatting at 1.2 Mb. But the drive (Chinon FR-506)
> > is a 1.2M one, and reads fine at 1.2M! Any clue? Is there a drive
> > setting that would prevent it to write at high density but let it do
> > at low density?
> At high density, have you taken a good look at pin 2 of the floppy 
> interface?  Have you checked to see if pin 2 is configured (via jumpers) 
> as "density select"?    Various drives have different jumperings for 
> pins 2 and 34 (and sometimes 4).  For example, I deal with some Japanese 
> CNC gear that uses pin 2 for disk change and pin 34 for read (and pin 4 
> for "in use".
> --Chuck
If formatting an already formatted disk, the format program will notlet you format a different density.Do note what I said earlier. Just formatting and writing to a 360K ona 1.2M drive can in some cases make it unusable on a 360K drive.The 1.2M drive does not erase the full width of a 360K track.When attempting to read on a 360K drive, there will be too much noisefrom the older track.If you are really interested in creating 360K disk, you must have a 360Kdrive.Dwight  		 	   		  

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