Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!uxc.cso.uiuc.edu!garcon!uxa.cso.uiuc.edu!sac90286
From: sac90286@uxa.cso.uiuc.edu (Kubla Khan)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Low Density Disks in High Densi
Message-ID: <1867@garcon.cso.uiuc.edu>
Date: 28 Aug 89 14:35:49 GMT
References: <291@bilver.UUCP> <45900267@uxe.cso.uiuc.edu>
Reply-To: kubla@uiuc.edu (Kubla Khan)
Organization: University of Illinois at Urbana-Champaign
Lines: 23

In article <9828@xanth.cs.odu.edu> rlb@cs.odu.edu (Robert L. Bailey) writes:
>>That doesn't explain why I am able to successfully read/write 360K diskettes
>>FORMATTED WITH A 360K DRIVE in my 1.2M drive! How does the 1.2M drive know not
>>to use high write current when writing data to a 360K disk?
>
>Simple.  When DOS logs in a new disk for the first time, it reads track 0.
>It then steps in 1 track and reads again.  If it is a high density drive
>with a 360K disk, the track number will still be 0.  If it is a HD drive
>with a 1.2M disk the track number will be 1.  
>
>Hope this clears up the confusion.

It certainly does, Bob; Thanks!

With that explanation, it's also clear why a disk formatted on a 360K drive and
written to by a 1.2M will often be readable on a 360K drive, whereas a 360K disk
formatted by a 1.2M drive to the low density format is often unreadable on
low density drives - the 360K drives have trouble accurately tracking the 
narrower tracks written by the HD drive. Right?


Scott
kubla@uiuc.edu