From: kegs@provalid.com   
      
   In article <4c3663fa-4d3e-4715-9b11-b6df9e4bca9an@googlegroups.com>,   
   engrav   wrote:   
   >Hi   
   >Have Powerbook 180, Powerbook G3 and Apple //e with external 3.5 hard   
   >drive.  I can format a 3.5 disk ProDOS on all 3 machines.  But...   
   >   
   >The disks are not interchangeable.  That is, for example, the disk   
   >formatted on the G3 cannot be read by the Apple //e.  Etc.   
   >   
   >Why is this?  I did something wrong?  I am missing something?   
   >   
   >Thanks   
   >   
   >Loren Engrav   
      
   There are many possible issues.  One is that 3.5" drives that are capable   
   of using 1.44MB have smaller heads.  These smaller heads write a smaller   
   track (in terms of width) even when writing to 800KB disks.  They can then   
   read back those disks fine--but a true 800KB drive might not.  True 800KB   
   drives have a "wider" head that is confused by the data the 1.44MB drive   
   didn't write, and so cannot read data written by a 1.44MB drive.  I never dealt   
   with this much, but I remember it being easy to read 800KB Apple II disks   
   on a Mac, but harder to go the other way (I would try to use a really old   
   Mac which only had an 800KB drive).  There may be some setting on the Mac   
   to make it write in a more compatible way to 800KB disks.   
      
   I also remember 1.44MB disks are generally not usable on an Apple II.  I think   
   a brand new disk would work, but once a true 1.44MB drive has written to it   
   in 1.44MB format, it's "infected" and an 800KB drive cannot overwrite it   
   properly.  I honestly don't remember the details, but there was definitely   
   some problem.   
      
   Kent   
      
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