Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!leah!rpi!crdgw1!ge-dab!peora!tarpit!bilver!bill
From: bill@bilver.UUCP (Bill Vermillion)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Low Density Disks in High Density Drives
Keywords: HD Disk 1.2M 360K
Message-ID: <291@bilver.UUCP>
Date: 23 Aug 89 14:13:38 GMT
References: <1293@cbnewsd.ATT.COM> <1836@garcon.cso.uiuc.edu>
Reply-To: bill@.UUCP (Bill Vermillion)
Organization: W. J. Vermillion, Winter Park, FL
Lines: 34

In article <1836@garcon.cso.uiuc.edu> kubla@uiuc.edu (Kubla Khan) writes:
>In article <1293@cbnewsd.ATT.COM> bryan@cbnewsd.ATT.COM (bryan.k.delaney) writes:
>>1.2M disks require a different write current
>>than the 360/720K disks so you should not use them at 360/720K
>>either.  
>
>This raises yet another question: I have a 1.2M 5-1/4" drive in my AT clone.
>It is able to read/write low density 360K diskettes (using the 360K format)
>with no problems, and I swap 360K diskettes with my XT clone all the time
>with no problems. How does the 1.2M drive know to change its write current
>in order to successfully write a 360K floppy? Or, if it does not change its
>write current, the how do you explain the ability of thousands to read/write
>low density floppies in their high density drives?

That's simple.  Part of the formatting routine.  You format HD and it goes to
the higher current.  DD and it uses the lower.   If the disks had been made
different for hd/dd the problems might not exist. 

That is what TRIED to be done for the 3.5s.  Put a hole in the disk to tell it
HD, no hole it is DD.

At one time, where there were almost no DS 5.25" drives some people used to
cut another notch and another index hole.  Then one drive mfr got wise and put
in two sensor and two index leds and had a flipply drive.  There is always
someone wanting to get more out of a disk than it was designed for.

If you want to do that, fine.  But be sure you understand what you are doing
and the consequences.  Just because disks look alike doesn't mean they are.


-- 
Bill Vermillion - UUCP: {uiucuxc,hoptoad,petsd}!peora!tarpit!bilver!bill
                      : bill@bilver.UUCP
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