From: et472@FreeNet.Carleton.CA   
      
   Knut Roll-Lund (kr-lund@nogarbage.online.no) writes:   
   > Michael Black wrote:   
   >> Dave Griffith (dgriffi@cs.csbuak.edu) writes:   
   >>   
   >>>Richard VanHouten  wrote:   
   >>>   
   >>>>I seem to recall that the original Mac floppy drives were 3.5" 180k   
   >>>>drives.  If these are those, they won't be compatible with anything else.   
   >>>   
   >>>No.  The original Mac floppies were 400k   
   >>>   
   >>   
   >> Yes.   
   >>   
   >> Single sided 3.5" would have been 400k (for the Macintosh) or 360K for   
   >> the "IBM PC types".   
   >   
   >   
   > So was the AppleII 3.5" drives too (400K) (and also 1.4M later). The   
   > 400k apple drives are special; they have a special card that does a   
   > completely different format (encoding). This is similar to the DiskII   
   > 5.25" drives. BTW AppleII is not Macintosh although they shared the 400K   
   > drive format.   
   >   
   >>   
   >> Single density and single sided 3.5" drives would have given about 180K.   
   >   
   > how? Per side, it was normal to use 10 sectors of 256 bytes in single   
   > density. In double density one would either have 18 sectors of 256 bytes   
   > or 9 sectors of 512 bytes.   
   >   
   I didn't do any calculations, but based it on 5.25" DD DS being 360K.   
   The 3.5" had twice as many tracks, yet basically the same storage capacity   
   on one side.  So if a single sided 3.5" double density floppy provided   
   360K or 400K depending on the computer (and when the other side came online   
   those would double), then single density would be around 180K.   
      
   I don't have the model 100 manuals handy, so I can't tell you exactly   
   how much storage they used, but it was pretty low.   
      
      MIchael   
      
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