Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!husc6!bbn!uwmcsd1!marque!gryphon!greg
From: greg@gryphon.CTS.COM (Greg Laskin)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Disk holes and other strange things (was Re: F-15 Strike Eag)
Message-ID: <2660@gryphon.CTS.COM>
Date: 20 Feb 88 17:08:55 GMT
References: <3037@cup.portal.com> <3186@cup.portal.com> <3255@cup.portal.com> <1412@puff.cs.wisc.edu>
Reply-To: greg@gryphon.CTS.COM (Greg Laskin)
Organization: Trailing Edge Technology, Redondo Beach, CA
Lines: 32

In article <1412@puff.cs.wisc.edu> ttang@puff.cs.wisc.edu (Theodore Tang) writes:
>The index hole on the floppy disk is used only for formatting purposes so all
>tracks remain in sync.  When the disk is read, the hole is not used.  I'm not
>sure about writes.
>
Don't do a term paper on index holes without some more research.

The index hole to which you refer, as opposed to index holes that
demarcate sectors on a hard sectored diskette, allows the controller
to determine:
   1)  That the diskette is moving.
   2)  That the diskette has made a complete revolution (the hole went by
       twice.)
In addition, it provides a convenient start-of-track reference marker
when formatting the diskette.  Diskette tracks are not in sync with
anything, by the way.

If, for example, you were looking for sector 4 and two index holes
went by, it would be a good bet that you weren't going to find sector 4.
Thanks to our friend, the hole, sectors don't have to be recorded
sequentially on the diskette.

If you see two index holes while formatting a track, you've written too
much formatting on the track, although many controllers don't recognize
this one.

-- 
Greg Laskin           
"When everybody's talking and nobody's listening, how can we decide?"
INTERNET:     Greg.Laskin@gryphon.CTS.COM
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