Path: utzoo!attcan!uunet!pilchuck!dataio!shiloh!fnx!del
From: del@fnx.UUCP (Dag Erik Lindberg)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Index hole on diskettes
Message-ID: <581@fnx.UUCP>
Date: 1 Jun 90 21:47:05 GMT
References: <9625@hydra.gatech.EDU> <3000@se-sd.SanDiego.NCR.COM>
Reply-To: del@fnx.UUCP (Dag Erik Lindberg)
Organization: I/Ovations    Kirkland, WA
Lines: 35

In article <3000@se-sd.SanDiego.NCR.COM> lord@se-sd.SanDiego.NCR.COM (Dave Lord) writes:
=In article <9625@hydra.gatech.EDU> ce1zzes@prism.gatech.EDU (Eric Sheppard) writes:
=}on an IBM diskette, the small hole near the center of the diskette is used
=}to indicate A) the start of a track B) the start of a sector.
=
=}My answer (B) was judged incorrect, and my debate with the instructor would
=
=}what they USED to do, until they developed soft sectoring.  The index hole
=}shows where the FIRST sector is located, and it's up to the DOS to determine
=}where the rest are.
=
=Sounds to me like you're the one who's out to lunch here. You admit that
=the index hole marks the start of the first sector but deny that it
=marks the start of a track? I can see why your professor is not buying.

The index hole does not necessarily indicate the start of the FIRST sector.
It does indicate the start of the track.  Define "IBM diskette".  If you
mean a diskette as formatted on an IBM PC compatible computer running PC DOS
then coincidently the index hole will also indicate the start of the first
sector.  However, the IBM specification does not require this, and you can
get improved performance by formatting the diskette with 'sector skew', this
is in addition to 'sector interleave'.  The sector skew is the offset from
the start of the first track to the first sector on the track.  This allows
for the step motion of the head to stabilize before the first sector of the
track comes around under the head.  Using this method of formatting (and
several systems do) results in a different sector being located following
the index hole on consecutive tracks!  These disks follow the IBM
specification, and can be read/written on PC clone machines running 'DOS'
with slightly improved performance over the 'normal' formatting scheme.


-- 
del AKA Erik Lindberg

uunet!pilchuck!fnx!del