Path: utzoo!mnetor!uunet!husc6!bbn!rochester!rutgers!mtune!mtunx!whuts!homxb!homxc!rps
From: rps@homxc.UUCP (R.SHARPLES)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Do 1.44Mb 3.5" drives reliably read/write 720K floppies?
Message-ID: <1528@homxc.UUCP>
Date: 14 Mar 88 14:14:32 GMT
References: <746@esunix.UUCP>
Distribution: na
Organization: AT&T Bell Laboratories, Holmdel
Lines: 51
Keywords: 3.5", disk formats, interchangeable
Summary: Problems with 1.44meg and 720K

In article <746@esunix.UUCP>, angerhof@esunix.UUCP (Norman Angerhofer) writes:
> I would like to put a 3.5" floppy drive into an AT-clone (which will hopefully
> have the BIOS to support this kind of drive.)
...
> 
> My question:  do the 1.44MB 3.5" drives also RELIABLY read and write the
> 720k format?
> 
> Thanks,
> 
> --Norman

I have just done this in my PC's Limited 386/16.  I have yet to get it
to work properly.  The PCL supports 720 and 1.44meg in its system setup.
I bought a Mitsubishi 1.44meg drive from Eltek (not recommended, the 
drive arrived without paperwork or hardware, they sent hardware but they
claim there is no paperwork - makes it fun trying to set the jumpers).
I also bought DOS 3.3 to support the 1.44meg formatting.

I had to set the system setup as a 1.44meg on drive B, if set as 720K
the system cries foul on boot and asks me to correct the error.
If I boot DOS 3.3 in the A drive (my hd is 3.2) it can read/write/format
the B drive as 1.44meg (even on 720K floppies).  However, if you follow
the MS DOS directions for formatting a 1.44meg as 720K:
	format b: /t:80 /n:9
you get the error "invalid parameter".  According to someone at the 
MS help #, this is an acknowledged bug - e.g. you can not format a 
1.44meg as 720K under DOS 3.3 at this time.  (I am not sure he knew
what he was talking about.)

HOWEVER, I am not at all sure that the drive is installed correctly.  If
you place a formatted 720K disk in it, it will read it fine.  If you 
try to write to it, it will clobber the disk.  Perhaps some jumper 
must be set, I don't know.  The MS support person readily admitted
that there was a problem in DOS 3.3 but seemed to have little understanding
of what that problem might be.  I think the problem is that either 
DOS can not tell the drive to, or the drive cannot switch to the 
lower density format (on 1.2 meg drives this involves a different speed
as well as track spacing).  This may be controlled by one of the 
mysterious jumpers on the drive.

So, anyone else have a clue?

Russ Sharples
homxc!rps

NOTE:

The above in NO WAY reflects the opinions of AT&T.
These opinions are my own and the results of un-scientific and 
highly irregular analysis methods.