Path: utzoo!mnetor!uunet!husc6!rutgers!clyde!cbosgd!mandrill!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Norton Speed Disk Bug and Fix?
Message-ID: <990@neoucom.UUCP>
Date: 7 Feb 88 02:01:53 GMT
References: <327@ttrdf.UUCP> <2023@bsu-cs.UUCP>
Sender: wfd@neoucom.UUCP
Organization: Northeastern Ohio Universities College of Medicine
Lines: 49
Keywords: Speed Disk Bug
Summary: Is this problem possibly related to so-called `sector creep'?


I have read several times and have seen discussed on this network,
a phenomenon referred to as sector creep.  Apparently, sector creep
is a cumulative phenomenon that causes disk data errors after
extended time has passed.

In a nutshell, there are guard bands of sync data recorded between
data sectors on a disk.  Due to physical limitations of the
controller electronics and instantaneous rotational instability of
the media, it is quite likely that part of the guard band will be
overwritten by rewrites of the sector.  Controller designers and
O/S writers are aware of sector creep and normally design guard
bands between sectors that assure many rewrites without danger of
the secotrs running into each other.

Over time, however, it is possible that the guard bands could be
completely overwritten and sectors begin to overlap on a heavily
used disk.  Norton Utilities' speeddisk program could accelerate
creep problems on an aging disk possibly since it is moving data
around a lot to unfragment files.

Recently I ran into what I suspect is a case of sector creep on an
IBM XT computer that has been in service for about four years.
One day, the file allocation table became unreadable on the XT's 10
meg drive.  The software on the machine hadn't been changed for
many months, and has not bothered other machines running the same
software mix.  Doing a low level format restored the drive to its
original usability.

Note that to get rid of sector creep, it is necessary to perform a
low level format.  For IBM ATs there is a program available on the
advanced diagnostics disk.  For HDU controllers from many companies
that have on-board bios chips, you can use DOS' debug to call a
low-level format routine from the BIOS ROM.  Run debug, and type
g=c800:005 at the prompt.  Most formatting routines have a menu
that makes the job pretty easy.  You'll probably need to know the
type number for your disk drive and if it requires write
precompensation; that data can be obtained from the drive
manufacturer.  Unfortunately sellers of clone machines seldom give
you sufficient information on the hard disk on your clone.  When
our lab people here buy clone machines, I ask them to have the
clone seller provide information necessary to do the low level
format.

In most versions of [MS]DOS, a DOS level format only does a surface
scan and zeroing of the FAT and root directory.  Early versions of
AT&T and Compaq are exceptions to the above.

--Bill