Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!nrl-cmf!cmcl2!brl-adm!umd5!uvaarpa!mcnc!ecsvax!mjg
From: mjg@ecsvax.UUCP (Michael Gingell)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Disk holes and other strange things (was Re: F-15 Strike Eag)
Message-ID: <4709@ecsvax.UUCP>
Date: 2 Mar 88 14:15:46 GMT
References: <3037@cup.portal.com> <3186@cup.portal.com> <3255@cup.portal.com> <1412@puff.cs.wisc.edu>
Organization: UNC Educational Computing Service
Lines: 20
Summary: New disk drives wont work without the hole

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.
> 
> 
Perfectly correct. The PC controller does not use the index hole if
it is reading or writing unless you have a bad disk. In that case
it may time out after a certain number of tries. 

On older disk drives you can actually cover the index hole with an
opaque write protect tab and still read or write. However you need
the index hole for formatting.

However modern half height disk drives have more sophisticated
electronics which times the intervals between successive index hole
pulses. If it is not 200 millisecs +/- 5% then the drive says to
itself "Oh - no disk in drive". It then lowers the drive ready line
and disables read/write signal lines.

Mike Gingell   ...ecsvax!mjg