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From: bill@bilver.uucp (Bill Vermillion)
Newsgroups: comp.sys.ibm.pc.hardware,comp.multimedia,comp.misc
Subject: Re: Diffs between DD & HD disks
Message-ID: <1991Apr12.182341.13589@bilver.uucp>
Date: 12 Apr 91 18:23:41 GMT
References: <1991Apr9.065832.16253@cs.ucla.edu> <1991Apr9.141703.5134@cs.dal.ca> <1991Apr9.191024.7048@cc.tut.fi>
Organization: W. J. Vermillion - Winter Park, FL
Lines: 37

In article <1991Apr9.191024.7048@cc.tut.fi> public@cc.tut.fi (PD Software Group) writes:
>
>In article <1991Apr9.141703.5134@cs.dal.ca> paixao@ug.cs.dal.ca (Nuno M. Paixao) writes:
>>I was using a machine with a high density 3.5" floppy in it, and wasn't aware 
>>that it was high density. Whenever I formatted a disk ( a DS/DD) I simply
>>typed FORMAT. The machine then formatted them to High density.
 
>There are some 3.5" drives which can't determine if the disk is DD or
>HD. Such drives are used at least on IBM PS -computers.

It is NOT the drive that is the problem in the PS computers, it is the
implementation.

IBM PS-2's look at the media to determine it is formatted or not, and then
proceed to format at the default unless you specify differently.

Other implementations look at the media housing to deterimine density by
seeingif the extra hole is there.  You can format 720's all day long at
1.44 in a PS2 environment.

One interesting sidelight showing the differences between implementation in
SOFTWARE on the same piece of harware was an IBM 80 I installed in a Xenix
application.

The floppy drive was defective.  But you would not know this under DOS.

You would type format with NO DISK under DOS and it would reject the format
command.  Under Xenix you would type format, the drive would turn on, the
drive would step all 80 tracks, and you would watch it through the door.

The hardware sensor indicating disk/no-disk failed in the disk in mode.
But IBM never checked that, as they don't check the density hole.


-- 
Bill Vermillion - UUCP: uunet!tarpit!bilver!bill
                      : bill@bilver.UUCP