Swapping Hi density drives for low density drives

[Michael B. Brutman]

The format bug is new to me, but I'm on DOS 3.3 anyway and DOS 3.3 does 
not have any problems if I used a genuine 720K drive on the Jr.  It does 
have problems if I use a 1.44MB drive instead.

Here it is in table format.  DOS 3.3 with no device drivers is always 
used and double density diskettes are always used.

Real 720K drive on Jr:
   Boots DOS 3.3 from original IBM DOS 3.3 diskette
   Formats other diskettes with no problems
   Boots DOS 3.3 from a double density copy of the original.
   Passes diagnostics

1.44MB drive on Jr:
   Boots DOS 3.3 from original IBM DOS 3.3 diskette
   Will not format other diskettes: gets invalid media error
   Diags runs but reports error.  (Probably related to above error)
   Diskette is readable - just track 0 has errors

A double density diskette prepared on a 'bigger' machine, whether it be 
by disk copy or diskette imaging program fails on the Jr when using the 
1.44MB drive.  These other machines all have 1.44MB drives.  Even though 
it fails on the Jr, it boots the other machines, so the diskette is fine.

I suspect some sort of timing error when the 1.44MB drives talk to the 
Jr controller.  I know I've used an ancient 1.44MB drive before ..  all 
of the drives I tried this time around are newer.  I'm wondering if 
something has changed in the manufacturing/design of the more modern 
drives that make them less tolerant or more error prone when using 
double density media.  It's not like people test double density media 
often anymore. :-)

I'm not bulk erasing ..  I'd better go find a bulk eraser to be sure.

720K drives are tough to find.  I'm going to try the strange Teac model 
and dumb it down to a 720.

Explain the drives on the JX - I thought those were 720 3.5 inch drives. 
  Are the SA465 and Teac 55F 5.25 or 3.5" drives?

Yes, the Qume 142s suck.  Besides being slow mechanically they are not 
much better than the old full height Tandons - just different glitches. 
  The drive rails always seem to get sticky, and they are noisy little 
A#@$@..  :-)



Mike