From: darylb@sword.eng.hou.compaq.com (Daryl Biberdorf)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Problem:  SE formats HD floppy as DD, but LC rejects it...why?
Date: 19 Aug 92 19:17:12 GMT
Article-I.D.: twisto.1992Aug19.191712.23972
Organization: Compaq Computer Corp.

In article <4947@blue.cis.pitt.edu.UUCP> macman+@pitt.edu (Dennis H Lippert) writes:
>In article <p59mj6j.bskendig@netcom.com> bskendig@netcom.com (Brian Kendig) writes:
>>In article <1992Aug17.200351.2274@twisto.eng.hou.compaq.com> darylb@sword.eng.hou.compaq.com (Daryl Biberdorf) writes:
>>>DOS machines routinely
>>>"adapt" to the format of the floppy inserted into the drive,
>>>provided the drive is capable of writing the format the disk is
>>>using.  My 1.4 MB drive has no problem at all recognizing and properly
>>>using 720K diskettes without being told which it is.
>
>A few comments on both of these cited articles...
>
>First, a DOS machine will "routinely adapt" to a *correctly formatted*
>disk... i.e. it knows 720k from 1.44m, but it does this "check" by
>way of the hole in the disk.  A DOS machine will *not* routinely adapt
>to a 720k disk incorrectly formatted 1.4m, nor the opposite case.

None of the DOS machines I've used (PS/2s, Compaqs, and several no-names)
have either the density sense mechanism (the switch that checks for the
hole in the diskette) or the media sense mechanism (that checks for
the presence of the diskette in the drive). 

They do *not* check the capacity of the diskette.  I just verified this by
placing a DD 3.5" diskette into my 3.5" HD drive and formatting it.
The DOS FORMAT command attempts to use the highest density that the
*drive* is capable of using.  Thus, a 3.5" DD diskette formatted in
a 3.5" HD drive will default to HD unless I use the density parameter
on the FORMAT command.  Please note that formatting a DD disk to HD
usually results in LOTS of bad sectors.

>Second, some DOS machines are not quite as smart as they look... 
>(possibly all, but I only have extensive knowledge of our (ugh!) Zeniths).
>What I mean is that the drive will "automatically" format 1.44m (unless
>you add the /n:9/t:80 parameters to the FORMAT).  The machine will then 
>cough up an error message when the 720k disk is "unformattable".

This is essentially what I repeated above.

>>Huh?  I use a PS/2 tower machine, and no matter what kind of disk I
>>put in the drive, when I enter the 'format' command, it _always_ tries
>>to format the disk as high density.  Then I always have to go fishing
>>for the DOS manual so I can remember the command-line option to make
>>the machine format the disk at the correct density.
>
>This is a quirk of PS-2's.  We have them in one lab here at Pitt (they're
>moving to *my* lab within a few weeks...) and they frankly don't give
>a damn how they format any disk.  (720 as 1.44m & vice-versa).  This 
>causes all kinds of hell for us, we send users back to that lab to
>get it fixed (720 as 1.44 format most common.... if 1.44 as 720 format
>we can cover the hole w/tape and fix it ourselves.)

Again, by default a DOS machine attempts to use the highest density
the DRIVE is capable of when formatting a diskette, unless you tell
it otherwise.  On DOS machines, there is no need to cover the hole
on a HD diskette (1.44 MB) formatted as 720K to "trick" the machine
into reading the diskette.  DOS machines "adapt" to the different
format automatically.

>I think IBM made a big boo-boo a few years back, they should fix it
>sometime!

I think the topic here is getting confused.  The problem is that if a user
formats a HD diskette as DD, a Mac with a HD drive will not correctly
read the diskette, because it detects that the diskette is a HD diskette
but does not detect the lower capacity format.  IMHO, Apple should
fix this.

Daryl
--
Daryl Biberdorf                 |  Compaq Computer Corporation | standard
darylb@sword.eng.hou.compaq.com |  20555 SH 249  M/S 060701    | disclaimer
dlb5404@tamsun.tamu.edu         |  Houston, TX 77070           | applies
Xref: sparky comp.sys.mac.hardware:15215 comp.sys.mac.system:10935 comp.sys.mac.wanted:7518